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 $241.29   9.751%   $264.8182   $264.82   $264.80   $264.80  
  Purchase #2 $166.57   3.226%   $171.9435   $171.94   $171.95   $171.90  
  Purchase #3 $113.49   10.355%   $125.2419   $125.24   $125.25   $125.20  
  Purchase #4 $46.78   6.861%   $49.9896   $49.99   $50.00   $50.00  
  Purchase #5 $195.66   3.650%   $202.8016   $202.80   $202.80   $202.80  
  Purchase #6 $149.65   8.608%   $162.5319   $162.53   $162.55   $162.50  
  Purchase #7 $8.93   9.507%   $9.779   $9.78   $9.80   $9.80  
  7 purchase totals = $922.37       $987.1057   $987.10   $987.15   $987.00