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 $67.99   8.289%   $73.6257   $73.63   $73.65   $73.60  
  Purchase #2 $150.25   10.648%   $166.2486   $166.25   $166.25   $166.20  
  Purchase #3 $143.30   11.337%   $159.5459   $159.55   $159.55   $159.50  
  Purchase #4 $189.40   9.428%   $207.2566   $207.26   $207.25   $207.30  
  Purchase #5 $8.90   3.429%   $9.2052   $9.21   $9.20   $9.20  
  Purchase #6 $162.67   5.748%   $172.0203   $172.02   $172.00   $172.00  
  Purchase #7 $135.75   6.753%   $144.9172   $144.92   $144.90   $144.90  
  7 purchase totals = $858.26       $932.8195   $932.84   $932.80   $932.70