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 $34.25   8.621%   $37.2027   $37.20   $37.20   $37.20  
  Purchase #2 $236.37   7.460%   $254.0032   $254.00   $254.00   $254.00  
  Purchase #3 $163.99   11.431%   $182.7357   $182.74   $182.75   $182.70  
  Purchase #4 $94.68   3.428%   $97.9256   $97.93   $97.95   $97.90  
  Purchase #5 $243.27   5.262%   $256.0709   $256.07   $256.05   $256.10  
  Purchase #6 $23.59   4.220%   $24.5855   $24.59   $24.60   $24.60  
  Purchase #7 $117.44   6.169%   $124.6849   $124.68   $124.70   $124.70  
  7 purchase totals = $913.59       $977.2085   $977.21   $977.25   $977.20