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 $28.98   12.773%   $32.6816   $32.68   $32.70   $32.70  
  Purchase #2 $172.47   7.774%   $185.8778   $185.88   $185.90   $185.90  
  Purchase #3 $78.70   11.150%   $87.4751   $87.48   $87.50   $87.50  
  Purchase #4 $125.93   5.174%   $132.4456   $132.45   $132.45   $132.40  
  Purchase #5 $163.87   7.447%   $176.0734   $176.07   $176.05   $176.10  
  Purchase #6 $101.53   12.689%   $114.4131   $114.41   $114.40   $114.40  
  Purchase #7 $28.86   8.568%   $31.3327   $31.33   $31.35   $31.30  
  7 purchase totals = $700.34       $760.2993   $760.30   $760.35   $760.30