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 $64.76   13.424%   $73.4534   $73.45   $73.45   $73.50  
  Purchase #2 $244.78   6.303%   $260.2085   $260.21   $260.20   $260.20  
  Purchase #3 $198.58   7.593%   $213.6582   $213.66   $213.65   $213.70  
  Purchase #4 $175.63   8.319%   $190.2407   $190.24   $190.25   $190.20  
  Purchase #5 $219.82   11.416%   $244.9147   $244.91   $244.90   $244.90  
  Purchase #6 $33.78   5.228%   $35.546   $35.55   $35.55   $35.50  
  Purchase #7 $248.83   6.566%   $265.1682   $265.17   $265.15   $265.20  
  7 purchase totals = $1,186.18       $1,283.1897   $1,283.19   $1,283.15   $1,283.20