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 $210.49   11.148%   $233.9554   $233.96   $233.95   $234.00  
  Purchase #2 $204.35   13.514%   $231.9659   $231.97   $231.95   $232.00  
  Purchase #3 $40.50   12.591%   $45.5994   $45.60   $45.60   $45.60  
  Purchase #4 $157.73   6.627%   $168.1828   $168.18   $168.20   $168.20  
  Purchase #5 $115.86   8.719%   $125.9618   $125.96   $125.95   $126.00  
  Purchase #6 $96.34   9.223%   $105.2254   $105.23   $105.25   $105.20  
  Purchase #7 $159.65   6.645%   $170.2587   $170.26   $170.25   $170.30  
  7 purchase totals = $984.92       $1,081.1494   $1,081.16   $1,081.15   $1,081.30