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 $106.74   4.784%   $111.8464   $111.85   $111.85   $111.80  
  Purchase #2 $213.62   12.187%   $239.6539   $239.65   $239.65   $239.70  
  Purchase #3 $250.32   4.339%   $261.1814   $261.18   $261.20   $261.20  
  Purchase #4 $29.80   12.845%   $33.6278   $33.63   $33.65   $33.60  
  Purchase #5 $175.77   11.471%   $195.9326   $195.93   $195.95   $195.90  
  Purchase #6 $33.67   4.232%   $35.0949   $35.09   $35.10   $35.10  
  Purchase #7 $62.47   7.212%   $66.9753   $66.98   $67.00   $67.00  
  7 purchase totals = $872.39       $944.3123   $944.31   $944.40   $944.30