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 $84.56   8.630%   $91.8575   $91.86   $91.85   $91.90  
  Purchase #2 $60.98   8.837%   $66.3688   $66.37   $66.35   $66.40  
  Purchase #3 $235.90   3.532%   $244.232   $244.23   $244.25   $244.20  
  Purchase #4 $63.95   7.460%   $68.7207   $68.72   $68.70   $68.70  
  Purchase #5 $71.56   8.223%   $77.4444   $77.44   $77.45   $77.40  
  Purchase #6 $231.43   11.421%   $257.8616   $257.86   $257.85   $257.90  
  Purchase #7 $240.64   8.808%   $261.8356   $261.84   $261.85   $261.80  
  7 purchase totals = $989.02       $1,068.3206   $1,068.32   $1,068.30   $1,068.30