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 $135.74   8.180%   $146.8435   $146.84   $146.85   $146.80  
  Purchase #2 $183.27   11.621%   $204.5678   $204.57   $204.55   $204.60  
  Purchase #3 $104.71   7.231%   $112.2816   $112.28   $112.30   $112.30  
  Purchase #4 $172.98   7.454%   $185.8739   $185.87   $185.85   $185.90  
  Purchase #5 $217.56   3.137%   $224.3849   $224.38   $224.40   $224.40  
  Purchase #6 $34.48   3.525%   $35.6954   $35.70   $35.70   $35.70  
  Purchase #7 $135.67   7.324%   $145.6065   $145.61   $145.60   $145.60  
  7 purchase totals = $984.41       $1,055.2536   $1,055.25   $1,055.25   $1,055.30