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 $83.84   12.483%   $94.3057   $94.31   $94.30   $94.30  
  Purchase #2 $152.87   10.665%   $169.1736   $169.17   $169.15   $169.20  
  Purchase #3 $54.55   6.164%   $57.9125   $57.91   $57.90   $57.90  
  Purchase #4 $182.91   8.307%   $198.1043   $198.10   $198.10   $198.10  
  Purchase #5 $200.93   11.815%   $224.6699   $224.67   $224.65   $224.70  
  Purchase #6 $57.29   8.709%   $62.2794   $62.28   $62.30   $62.30  
  Purchase #7 $224.80   5.482%   $237.1235   $237.12   $237.10   $237.10  
  7 purchase totals = $957.19       $1,043.5689   $1,043.56   $1,043.50   $1,043.60