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 $241.45   11.717%   $269.7407   $269.74   $269.75   $269.70  
  Purchase #2 $248.28   7.582%   $267.1046   $267.10   $267.10   $267.10  
  Purchase #3 $40.45   12.438%   $45.4812   $45.48   $45.50   $45.50  
  Purchase #4 $193.72   5.344%   $204.0724   $204.07   $204.05   $204.10  
  Purchase #5 $87.49   12.281%   $98.2346   $98.23   $98.25   $98.20  
  Purchase #6 $157.56   8.722%   $171.3024   $171.30   $171.30   $171.30  
  Purchase #7 $248.31   8.782%   $270.1166   $270.12   $270.10   $270.10  
  7 purchase totals = $1,217.26       $1,326.0525   $1,326.04   $1,326.05   $1,326.00