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 $150.74   13.569%   $171.1939   $171.19   $171.20   $171.20  
  Purchase #2 $13.56   8.820%   $14.756   $14.76   $14.75   $14.80  
  Purchase #3 $157.55   7.376%   $169.1709   $169.17   $169.15   $169.20  
  Purchase #4 $222.52   9.303%   $243.221   $243.22   $243.20   $243.20  
  Purchase #5 $100.84   3.637%   $104.5076   $104.51   $104.50   $104.50  
  Purchase #6 $87.60   8.457%   $95.0083   $95.01   $95.00   $95.00  
  Purchase #7 $151.57   11.371%   $168.805   $168.81   $168.80   $168.80  
  7 purchase totals = $884.38       $966.6627   $966.67   $966.60   $966.70