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 $91.77   6.401%   $97.6442   $97.64   $97.65   $97.60  
  Purchase #2 $102.65   11.522%   $114.4773   $114.48   $114.50   $114.50  
  Purchase #3 $203.60   11.496%   $227.0059   $227.01   $227.00   $227.00  
  Purchase #4 $196.66   11.288%   $218.859   $218.86   $218.85   $218.90  
  Purchase #5 $52.76   3.225%   $54.4615   $54.46   $54.45   $54.50  
  Purchase #6 $67.73   9.196%   $73.9585   $73.96   $73.95   $74.00  
  Purchase #7 $152.84   5.866%   $161.8056   $161.81   $161.80   $161.80  
  7 purchase totals = $868.01       $948.2120   $948.22   $948.20   $948.30