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 $58.87   8.142%   $63.6632   $63.66   $63.65   $63.70  
  Purchase #2 $223.98   8.317%   $242.6084   $242.61   $242.60   $242.60  
  Purchase #3 $132.85   5.375%   $139.9907   $139.99   $140.00   $140.00  
  Purchase #4 $197.63   12.453%   $222.2409   $222.24   $222.25   $222.20  
  Purchase #5 $37.92   8.864%   $41.2812   $41.28   $41.30   $41.30  
  Purchase #6 $79.42   12.695%   $89.5024   $89.50   $89.50   $89.50  
  Purchase #7 $101.27   4.821%   $106.1522   $106.15   $106.15   $106.20  
  7 purchase totals = $831.94       $905.4390   $905.43   $905.45   $905.50