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 $209.90   13.669%   $238.5912   $238.59   $238.60   $238.60  
  Purchase #2 $111.26   5.690%   $117.5907   $117.59   $117.60   $117.60  
  Purchase #3 $63.32   12.431%   $71.1913   $71.19   $71.20   $71.20  
  Purchase #4 $183.90   9.476%   $201.3264   $201.33   $201.35   $201.30  
  Purchase #5 $29.45   13.209%   $33.3401   $33.34   $33.35   $33.30  
  Purchase #6 $227.50   10.380%   $251.1145   $251.11   $251.10   $251.10  
  Purchase #7 $195.70   7.731%   $210.8296   $210.83   $210.85   $210.80  
  7 purchase totals = $1,021.03       $1,123.9838   $1,123.98   $1,124.05   $1,123.90