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 $82.36   11.399%   $91.7482   $91.75   $91.75   $91.70  
  Purchase #2 $16.98   9.514%   $18.5955   $18.60   $18.60   $18.60  
  Purchase #3 $101.57   12.440%   $114.2053   $114.21   $114.20   $114.20  
  Purchase #4 $123.54   10.289%   $136.251   $136.25   $136.25   $136.30  
  Purchase #5 $217.83   8.755%   $236.901   $236.90   $236.90   $236.90  
  Purchase #6 $223.27   10.275%   $246.211   $246.21   $246.20   $246.20  
  Purchase #7 $106.51   9.511%   $116.6402   $116.64   $116.65   $116.60  
  7 purchase totals = $872.06       $960.5522   $960.56   $960.55   $960.50