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 $66.96   3.756%   $69.475   $69.48   $69.50   $69.50  
  Purchase #2 $171.85   9.332%   $187.887   $187.89   $187.90   $187.90  
  Purchase #3 $50.76   9.130%   $55.3944   $55.39   $55.40   $55.40  
  Purchase #4 $93.29   11.868%   $104.3617   $104.36   $104.35   $104.40  
  Purchase #5 $161.72   13.519%   $183.5829   $183.58   $183.60   $183.60  
  Purchase #6 $215.53   11.626%   $240.5875   $240.59   $240.60   $240.60  
  Purchase #7 $113.76   7.149%   $121.8927   $121.89   $121.90   $121.90  
  7 purchase totals = $873.87       $963.1812   $963.18   $963.25   $963.30