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 $59.92   11.782%   $66.9798   $66.98   $67.00   $67.00  
  Purchase #2 $19.31   8.165%   $20.8867   $20.89   $20.90   $20.90  
  Purchase #3 $101.95   4.609%   $106.6489   $106.65   $106.65   $106.60  
  Purchase #4 $57.91   4.117%   $60.2942   $60.29   $60.30   $60.30  
  Purchase #5 $208.70   8.178%   $225.7675   $225.77   $225.75   $225.80  
  Purchase #6 $69.28   6.520%   $73.7971   $73.80   $73.80   $73.80  
  Purchase #7 $231.50   7.650%   $249.2098   $249.21   $249.20   $249.20  
  7 purchase totals = $748.57       $803.5840   $803.59   $803.60   $803.60