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 $55.33   8.371%   $59.9617   $59.96   $59.95   $60.00  
  Purchase #2 $72.95   9.317%   $79.7468   $79.75   $79.75   $79.70  
  Purchase #3 $108.63   5.612%   $114.7263   $114.73   $114.75   $114.70  
  Purchase #4 $212.89   4.562%   $222.602   $222.60   $222.60   $222.60  
  Purchase #5 $33.66   9.289%   $36.7867   $36.79   $36.80   $36.80  
  Purchase #6 $61.72   9.822%   $67.7821   $67.78   $67.80   $67.80  
  Purchase #7 $209.44   13.459%   $237.6285   $237.63   $237.65   $237.60  
  7 purchase totals = $754.62       $819.2341   $819.24   $819.30   $819.20