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 $10.57   6.681%   $11.2762   $11.28   $11.30   $11.30  
  Purchase #2 $234.97   6.590%   $250.4545   $250.45   $250.45   $250.50  
  Purchase #3 $232.90   3.600%   $241.2844   $241.28   $241.30   $241.30  
  Purchase #4 $72.55   4.399%   $75.7415   $75.74   $75.75   $75.70  
  Purchase #5 $236.80   12.561%   $266.5444   $266.54   $266.55   $266.50  
  Purchase #6 $12.87   4.463%   $13.4444   $13.44   $13.45   $13.40  
  Purchase #7 $131.78   5.459%   $138.9739   $138.97   $138.95   $139.00  
  7 purchase totals = $932.44       $997.7193   $997.70   $997.75   $997.70