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 $68.60   6.782%   $73.2525   $73.25   $73.25   $73.30  
  Purchase #2 $147.27   3.479%   $152.3935   $152.39   $152.40   $152.40  
  Purchase #3 $157.67   10.530%   $174.2727   $174.27   $174.25   $174.30  
  Purchase #4 $234.37   4.746%   $245.4932   $245.49   $245.50   $245.50  
  Purchase #5 $158.42   10.725%   $175.4105   $175.41   $175.40   $175.40  
  Purchase #6 $91.48   12.617%   $103.022   $103.02   $103.00   $103.00  
  Purchase #7 $213.57   13.405%   $242.1991   $242.20   $242.20   $242.20  
  7 purchase totals = $1,071.38       $1,166.0435   $1,166.03   $1,166.00   $1,166.10