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 $60.80   9.347%   $66.483   $66.48   $66.50   $66.50  
  Purchase #2 $246.39   11.363%   $274.3873   $274.39   $274.40   $274.40  
  Purchase #3 $30.73   11.528%   $34.2726   $34.27   $34.25   $34.30  
  Purchase #4 $213.90   3.712%   $221.84   $221.84   $221.85   $221.80  
  Purchase #5 $114.64   12.575%   $129.056   $129.06   $129.05   $129.10  
  Purchase #6 $92.86   12.595%   $104.5557   $104.56   $104.55   $104.60  
  Purchase #7 $196.61   11.175%   $218.5812   $218.58   $218.60   $218.60  
  7 purchase totals = $955.93       $1,049.1758   $1,049.18   $1,049.20   $1,049.30