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 $114.42   10.618%   $126.5691   $126.57   $126.55   $126.60  
  Purchase #2 $220.59   8.304%   $238.9078   $238.91   $238.90   $238.90  
  Purchase #3 $47.55   8.348%   $51.5195   $51.52   $51.50   $51.50  
  Purchase #4 $228.87   9.768%   $251.226   $251.23   $251.25   $251.20  
  Purchase #5 $82.46   6.647%   $87.9411   $87.94   $87.95   $87.90  
  Purchase #6 $64.99   11.174%   $72.252   $72.25   $72.25   $72.30  
  Purchase #7 $21.56   9.154%   $23.5336   $23.53   $23.55   $23.50  
  7 purchase totals = $780.44       $851.9491   $851.95   $851.95   $851.90