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 $92.85   4.251%   $96.7971   $96.80   $96.80   $96.80  
  Purchase #2 $23.91   6.347%   $25.4276   $25.43   $25.45   $25.40  
  Purchase #3 $223.49   4.727%   $234.0544   $234.05   $234.05   $234.10  
  Purchase #4 $187.48   3.231%   $193.5375   $193.54   $193.55   $193.50  
  Purchase #5 $215.53   4.794%   $225.8625   $225.86   $225.85   $225.90  
  Purchase #6 $56.86   9.526%   $62.2765   $62.28   $62.30   $62.30  
  Purchase #7 $112.43   5.778%   $118.9262   $118.93   $118.95   $118.90  
  7 purchase totals = $912.55       $956.8818   $956.89   $956.95   $956.90