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 $44.70   8.295%   $48.4079   $48.41   $48.40   $48.40  
  Purchase #2 $163.68   11.589%   $182.6489   $182.65   $182.65   $182.60  
  Purchase #3 $103.93   4.717%   $108.8324   $108.83   $108.85   $108.80  
  Purchase #4 $115.27   5.489%   $121.5972   $121.60   $121.60   $121.60  
  Purchase #5 $49.60   5.557%   $52.3563   $52.36   $52.35   $52.40  
  Purchase #6 $148.25   9.401%   $162.187   $162.19   $162.20   $162.20  
  Purchase #7 $182.29   8.394%   $197.5914   $197.59   $197.60   $197.60  
  7 purchase totals = $807.72       $873.6211   $873.63   $873.65   $873.60