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 $233.68   9.624%   $256.1694   $256.17   $256.15   $256.20  
  Purchase #2 $59.96   11.589%   $66.9088   $66.91   $66.90   $66.90  
  Purchase #3 $133.40   9.408%   $145.9503   $145.95   $145.95   $146.00  
  Purchase #4 $150.33   9.564%   $164.7076   $164.71   $164.70   $164.70  
  Purchase #5 $49.34   4.351%   $51.4868   $51.49   $51.50   $51.50  
  Purchase #6 $195.55   13.407%   $221.7674   $221.77   $221.75   $221.80  
  Purchase #7 $135.95   10.315%   $149.9732   $149.97   $149.95   $150.00  
  7 purchase totals = $958.21       $1,056.9635   $1,056.97   $1,056.90   $1,057.10