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 $201.36   11.575%   $224.6674   $224.67   $224.65   $224.70  
  Purchase #2 $152.42   4.759%   $159.6737   $159.67   $159.65   $159.70  
  Purchase #3 $53.90   8.174%   $58.3058   $58.31   $58.30   $58.30  
  Purchase #4 $198.83   8.588%   $215.9055   $215.91   $215.90   $215.90  
  Purchase #5 $224.54   3.643%   $232.72   $232.72   $232.70   $232.70  
  Purchase #6 $191.79   6.844%   $204.9161   $204.92   $204.90   $204.90  
  Purchase #7 $179.39   5.383%   $189.0466   $189.05   $189.05   $189.00  
  7 purchase totals = $1,202.23       $1,285.2351   $1,285.25   $1,285.15   $1,285.20