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 $118.41   12.464%   $133.1686   $133.17   $133.15   $133.20  
  Purchase #2 $229.91   8.288%   $248.9649   $248.96   $248.95   $249.00  
  Purchase #3 $118.76   5.698%   $125.5269   $125.53   $125.55   $125.50  
  Purchase #4 $240.98   3.644%   $249.7613   $249.76   $249.75   $249.80  
  Purchase #5 $207.99   12.741%   $234.49   $234.49   $234.50   $234.50  
  Purchase #6 $69.76   8.710%   $75.8361   $75.84   $75.85   $75.80  
  Purchase #7 $204.39   13.512%   $232.0072   $232.01   $232.00   $232.00  
  7 purchase totals = $1,190.20       $1,299.7550   $1,299.76   $1,299.75   $1,299.80