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 $205.87   8.606%   $223.5872   $223.59   $223.60   $223.60  
  Purchase #2 $191.69   12.554%   $215.7548   $215.75   $215.75   $215.80  
  Purchase #3 $19.82   4.583%   $20.7284   $20.73   $20.75   $20.70  
  Purchase #4 $201.77   10.807%   $223.5753   $223.58   $223.60   $223.60  
  Purchase #5 $64.29   7.600%   $69.176   $69.18   $69.20   $69.20  
  Purchase #6 $100.56   6.181%   $106.7756   $106.78   $106.80   $106.80  
  Purchase #7 $47.98   10.417%   $52.9781   $52.98   $53.00   $53.00  
  7 purchase totals = $831.98       $912.5754   $912.59   $912.70   $912.70