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 $244.58   9.344%   $267.4336   $267.43   $267.45   $267.40  
  Purchase #2 $164.78   10.212%   $181.6073   $181.61   $181.60   $181.60  
  Purchase #3 $46.36   3.472%   $47.9696   $47.97   $47.95   $48.00  
  Purchase #4 $242.31   7.743%   $261.0721   $261.07   $261.05   $261.10  
  Purchase #5 $43.64   7.389%   $46.8646   $46.86   $46.85   $46.90  
  Purchase #6 $48.98   10.168%   $53.9603   $53.96   $53.95   $54.00  
  Purchase #7 $68.82   3.397%   $71.1578   $71.16   $71.15   $71.20  
  7 purchase totals = $859.47       $930.0653   $930.06   $930.00   $930.20