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 $37.92   11.430%   $42.2543   $42.25   $42.25   $42.30  
  Purchase #2 $46.93   11.169%   $52.1716   $52.17   $52.15   $52.20  
  Purchase #3 $243.49   4.705%   $254.9462   $254.95   $254.95   $254.90  
  Purchase #4 $102.51   13.631%   $116.4831   $116.48   $116.50   $116.50  
  Purchase #5 $42.90   4.532%   $44.8442   $44.84   $44.85   $44.80  
  Purchase #6 $187.87   3.614%   $194.6596   $194.66   $194.65   $194.70  
  Purchase #7 $7.27   7.528%   $7.8173   $7.82   $7.80   $7.80  
  7 purchase totals = $668.89       $713.1763   $713.17   $713.15   $713.20