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 $246.50   6.273%   $261.9629   $261.96   $261.95   $262.00  
  Purchase #2 $158.92   12.221%   $178.3416   $178.34   $178.35   $178.30  
  Purchase #3 $239.99   6.471%   $255.5198   $255.52   $255.50   $255.50  
  Purchase #4 $228.59   6.830%   $244.2027   $244.20   $244.20   $244.20  
  Purchase #5 $228.85   8.630%   $248.5998   $248.60   $248.60   $248.60  
  Purchase #6 $63.39   13.178%   $71.7435   $71.74   $71.75   $71.70  
  Purchase #7 $55.33   13.417%   $62.7536   $62.75   $62.75   $62.80  
  7 purchase totals = $1,221.57       $1,323.1239   $1,323.11   $1,323.10   $1,323.10