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 $245.62   9.293%   $268.4455   $268.45   $268.45   $268.40  
  Purchase #2 $15.62   7.638%   $16.8131   $16.81   $16.80   $16.80  
  Purchase #3 $67.55   5.341%   $71.1578   $71.16   $71.15   $71.20  
  Purchase #4 $236.87   4.146%   $246.6906   $246.69   $246.70   $246.70  
  Purchase #5 $66.74   13.825%   $75.9668   $75.97   $75.95   $76.00  
  Purchase #6 $173.43   11.468%   $193.319   $193.32   $193.30   $193.30  
  Purchase #7 $167.79   13.378%   $190.2369   $190.24   $190.25   $190.20  
  7 purchase totals = $973.62       $1,062.6297   $1,062.64   $1,062.60   $1,062.60