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 $174.87   11.773%   $195.4574   $195.46   $195.45   $195.50  
  Purchase #2 $99.35   11.338%   $110.6143   $110.61   $110.60   $110.60  
  Purchase #3 $155.31   3.830%   $161.2584   $161.26   $161.25   $161.30  
  Purchase #4 $33.95   5.283%   $35.7436   $35.74   $35.75   $35.70  
  Purchase #5 $134.78   4.468%   $140.802   $140.80   $140.80   $140.80  
  Purchase #6 $119.75   9.785%   $131.4675   $131.47   $131.45   $131.50  
  Purchase #7 $114.42   3.263%   $118.1535   $118.15   $118.15   $118.20  
  7 purchase totals = $832.43       $893.4967   $893.49   $893.45   $893.60