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 $60.93   5.873%   $64.5084   $64.51   $64.50   $64.50  
  Purchase #2 $195.72   5.598%   $206.6764   $206.68   $206.70   $206.70  
  Purchase #3 $226.81   7.750%   $244.3878   $244.39   $244.40   $244.40  
  Purchase #4 $38.75   7.279%   $41.5706   $41.57   $41.55   $41.60  
  Purchase #5 $186.50   4.422%   $194.747   $194.75   $194.75   $194.70  
  Purchase #6 $84.77   3.210%   $87.4911   $87.49   $87.50   $87.50  
  Purchase #7 $108.94   9.417%   $119.1989   $119.20   $119.20   $119.20  
  7 purchase totals = $902.42       $958.5802   $958.59   $958.60   $958.60