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 $58.80   7.694%   $63.3241   $63.32   $63.30   $63.30  
  Purchase #2 $169.48   5.459%   $178.7319   $178.73   $178.75   $178.70  
  Purchase #3 $154.47   11.343%   $171.9915   $171.99   $172.00   $172.00  
  Purchase #4 $238.50   3.240%   $246.2274   $246.23   $246.25   $246.20  
  Purchase #5 $133.70   12.733%   $150.724   $150.72   $150.70   $150.70  
  Purchase #6 $219.75   12.107%   $246.3551   $246.36   $246.35   $246.40  
  Purchase #7 $124.71   9.761%   $136.8829   $136.88   $136.90   $136.90  
  7 purchase totals = $1,099.41       $1,194.2369   $1,194.23   $1,194.25   $1,194.20