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 $23.76   10.244%   $26.194   $26.19   $26.20   $26.20  
  Purchase #2 $234.90   6.333%   $249.7762   $249.78   $249.80   $249.80  
  Purchase #3 $102.53   9.740%   $112.5164   $112.52   $112.50   $112.50  
  Purchase #4 $240.56   12.347%   $270.2619   $270.26   $270.25   $270.30  
  Purchase #5 $138.79   9.488%   $151.9584   $151.96   $151.95   $152.00  
  Purchase #6 $200.36   13.612%   $227.633   $227.63   $227.65   $227.60  
  Purchase #7 $208.82   5.485%   $220.2738   $220.27   $220.25   $220.30  
  7 purchase totals = $1,149.72       $1,258.6137   $1,258.61   $1,258.60   $1,258.70