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 $111.55   7.117%   $119.489   $119.49   $119.50   $119.50  
  Purchase #2 $75.99   7.333%   $81.5623   $81.56   $81.55   $81.60  
  Purchase #3 $35.70   5.590%   $37.6956   $37.70   $37.70   $37.70  
  Purchase #4 $126.69   7.115%   $135.704   $135.70   $135.70   $135.70  
  Purchase #5 $112.46   11.258%   $125.1207   $125.12   $125.10   $125.10  
  Purchase #6 $245.90   11.421%   $273.9842   $273.98   $274.00   $274.00  
  Purchase #7 $233.43   12.391%   $262.3543   $262.35   $262.35   $262.40  
  7 purchase totals = $941.72       $1,035.9101   $1,035.90   $1,035.90   $1,036.00