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 $182.79   11.763%   $204.2916   $204.29   $204.30   $204.30  
  Purchase #2 $151.76   7.301%   $162.84   $162.84   $162.85   $162.80  
  Purchase #3 $60.35   13.692%   $68.6131   $68.61   $68.60   $68.60  
  Purchase #4 $32.64   5.830%   $34.5429   $34.54   $34.55   $34.50  
  Purchase #5 $151.71   11.779%   $169.5799   $169.58   $169.60   $169.60  
  Purchase #6 $55.81   6.803%   $59.6068   $59.61   $59.60   $59.60  
  Purchase #7 $156.45   4.612%   $163.6655   $163.67   $163.65   $163.70  
  7 purchase totals = $791.51       $863.1398   $863.14   $863.15   $863.10