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 $176.64   13.661%   $200.7708   $200.77   $200.75   $200.80  
  Purchase #2 $5.58   10.823%   $6.1839   $6.18   $6.20   $6.20  
  Purchase #3 $181.94   7.526%   $195.6328   $195.63   $195.65   $195.60  
  Purchase #4 $83.77   6.405%   $89.1355   $89.14   $89.15   $89.10  
  Purchase #5 $58.77   10.375%   $64.8674   $64.87   $64.85   $64.90  
  Purchase #6 $98.41   5.841%   $104.1581   $104.16   $104.15   $104.20  
  Purchase #7 $240.97   10.837%   $267.0839   $267.08   $267.10   $267.10  
  7 purchase totals = $846.08       $927.8324   $927.83   $927.85   $927.90