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 $233.55   5.266%   $245.8487   $245.85   $245.85   $245.80  
  Purchase #2 $79.98   5.809%   $84.626   $84.63   $84.65   $84.60  
  Purchase #3 $69.63   6.727%   $74.314   $74.31   $74.30   $74.30  
  Purchase #4 $162.55   6.524%   $173.1548   $173.15   $173.15   $173.20  
  Purchase #5 $236.74   3.333%   $244.6305   $244.63   $244.65   $244.60  
  Purchase #6 $127.40   6.820%   $136.0887   $136.09   $136.10   $136.10  
  Purchase #7 $61.99   4.389%   $64.7107   $64.71   $64.70   $64.70  
  7 purchase totals = $971.84       $1,023.3734   $1,023.37   $1,023.40   $1,023.30