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 $213.96   10.388%   $236.1862   $236.19   $236.20   $236.20  
  Purchase #2 $176.63   10.694%   $195.5188   $195.52   $195.50   $195.50  
  Purchase #3 $114.29   10.168%   $125.911   $125.91   $125.90   $125.90  
  Purchase #4 $175.99   10.681%   $194.7875   $194.79   $194.80   $194.80  
  Purchase #5 $28.93   12.406%   $32.5191   $32.52   $32.50   $32.50  
  Purchase #6 $29.38   10.427%   $32.4435   $32.44   $32.45   $32.40  
  Purchase #7 $247.59   5.251%   $260.591   $260.59   $260.60   $260.60  
  7 purchase totals = $986.77       $1,077.9571   $1,077.96   $1,077.95   $1,077.90