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 $29.63   9.120%   $32.3323   $32.33   $32.35   $32.30  
  Purchase #2 $195.74   10.599%   $216.4865   $216.49   $216.50   $216.50  
  Purchase #3 $35.30   8.771%   $38.3962   $38.40   $38.40   $38.40  
  Purchase #4 $101.96   4.234%   $106.277   $106.28   $106.30   $106.30  
  Purchase #5 $190.39   10.372%   $210.1373   $210.14   $210.15   $210.10  
  Purchase #6 $94.43   10.585%   $104.4254   $104.43   $104.45   $104.40  
  Purchase #7 $60.48   3.437%   $62.5587   $62.56   $62.55   $62.60  
  7 purchase totals = $707.93       $770.6134   $770.63   $770.70   $770.60