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 $208.94   3.815%   $216.9111   $216.91   $216.90   $216.90  
  Purchase #2 $103.81   11.792%   $116.0513   $116.05   $116.05   $116.10  
  Purchase #3 $211.53   11.362%   $235.564   $235.56   $235.55   $235.60  
  Purchase #4 $62.84   5.697%   $66.42   $66.42   $66.40   $66.40  
  Purchase #5 $74.28   10.412%   $82.014   $82.01   $82.00   $82.00  
  Purchase #6 $111.87   3.135%   $115.3771   $115.38   $115.40   $115.40  
  Purchase #7 $122.63   9.334%   $134.0763   $134.08   $134.10   $134.10  
  7 purchase totals = $895.90       $966.4138   $966.41   $966.40   $966.50