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 $218.42   3.262%   $225.5449   $225.54   $225.55   $225.50  
  Purchase #2 $66.70   13.591%   $75.7652   $75.77   $75.75   $75.80  
  Purchase #3 $45.81   11.223%   $50.9513   $50.95   $50.95   $51.00  
  Purchase #4 $212.83   8.583%   $231.0972   $231.10   $231.10   $231.10  
  Purchase #5 $213.47   10.468%   $235.816   $235.82   $235.80   $235.80  
  Purchase #6 $240.62   6.317%   $255.82   $255.82   $255.80   $255.80  
  Purchase #7 $245.41   6.846%   $262.2108   $262.21   $262.20   $262.20  
  7 purchase totals = $1,243.26       $1,337.2054   $1,337.21   $1,337.15   $1,337.20