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 $123.34   7.789%   $132.947   $132.95   $132.95   $132.90  
  Purchase #2 $61.61   6.650%   $65.7071   $65.71   $65.70   $65.70  
  Purchase #3 $103.67   4.554%   $108.3911   $108.39   $108.40   $108.40  
  Purchase #4 $109.88   11.866%   $122.9184   $122.92   $122.90   $122.90  
  Purchase #5 $199.59   8.604%   $216.7627   $216.76   $216.75   $216.80  
  Purchase #6 $160.57   6.139%   $170.4274   $170.43   $170.45   $170.40  
  Purchase #7 $227.73   8.365%   $246.7796   $246.78   $246.80   $246.80  
  7 purchase totals = $986.39       $1,063.9333   $1,063.94   $1,063.95   $1,063.90