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 $59.73   8.733%   $64.9462   $64.95   $64.95   $64.90  
  Purchase #2 $57.49   7.433%   $61.7632   $61.76   $61.75   $61.80  
  Purchase #3 $244.89   9.608%   $268.419   $268.42   $268.40   $268.40  
  Purchase #4 $167.48   5.387%   $176.5021   $176.50   $176.50   $176.50  
  Purchase #5 $124.83   3.851%   $129.6372   $129.64   $129.65   $129.60  
  Purchase #6 $227.84   3.276%   $235.304   $235.30   $235.30   $235.30  
  Purchase #7 $195.43   7.356%   $209.8058   $209.81   $209.80   $209.80  
  7 purchase totals = $1,077.69       $1,146.3775   $1,146.38   $1,146.35   $1,146.30