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 $59.44   9.224%   $64.9227   $64.92   $64.90   $64.90  
  Purchase #2 $246.67   7.757%   $265.8042   $265.80   $265.80   $265.80  
  Purchase #3 $106.75   13.499%   $121.1602   $121.16   $121.15   $121.20  
  Purchase #4 $42.66   6.262%   $45.3314   $45.33   $45.35   $45.30  
  Purchase #5 $182.98   10.554%   $202.2917   $202.29   $202.30   $202.30  
  Purchase #6 $219.46   5.616%   $231.7849   $231.78   $231.80   $231.80  
  Purchase #7 $146.97   5.134%   $154.5154   $154.52   $154.50   $154.50  
  7 purchase totals = $1,004.93       $1,085.8105   $1,085.80   $1,085.80   $1,085.80