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 $245.55   3.656%   $254.5273   $254.53   $254.55   $254.50  
  Purchase #2 $146.72   10.414%   $161.9994   $162.00   $162.00   $162.00  
  Purchase #3 $224.86   8.658%   $244.3284   $244.33   $244.35   $244.30  
  Purchase #4 $95.94   4.548%   $100.3034   $100.30   $100.30   $100.30  
  Purchase #5 $87.28   11.488%   $97.3067   $97.31   $97.30   $97.30  
  Purchase #6 $114.34   6.218%   $121.4497   $121.45   $121.45   $121.40  
  Purchase #7 $43.70   10.607%   $48.3353   $48.34   $48.35   $48.30  
  7 purchase totals = $958.39       $1,028.2502   $1,028.26   $1,028.30   $1,028.10