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 $59.58   3.201%   $61.4872   $61.49   $61.50   $61.50  
  Purchase #2 $122.74   8.224%   $132.8341   $132.83   $132.85   $132.80  
  Purchase #3 $19.86   4.578%   $20.7692   $20.77   $20.75   $20.80  
  Purchase #4 $213.37   13.433%   $242.032   $242.03   $242.05   $242.00  
  Purchase #5 $94.75   5.387%   $99.8542   $99.85   $99.85   $99.90  
  Purchase #6 $164.60   13.730%   $187.1996   $187.20   $187.20   $187.20  
  Purchase #7 $96.79   8.274%   $104.7984   $104.80   $104.80   $104.80  
  7 purchase totals = $771.69       $848.9747   $848.97   $849.00   $849.00