Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $243.72   9.733%   $267.4413   $267.44   $267.45   $267.40  
  Purchase #2 $163.26   12.744%   $184.0659   $184.07   $184.05   $184.10  
  Purchase #3 $162.59   4.187%   $169.3976   $169.40   $169.40   $169.40  
  Purchase #4 $163.31   4.742%   $171.0542   $171.05   $171.05   $171.10  
  Purchase #5 $178.49   8.453%   $193.5778   $193.58   $193.60   $193.60  
  Purchase #6 $111.84   12.282%   $125.5762   $125.58   $125.60   $125.60  
  Purchase #7 $120.62   4.144%   $125.6185   $125.62   $125.60   $125.60  
  7 purchase totals = $1,143.83       $1,236.7315   $1,236.74   $1,236.75   $1,236.80