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 $231.29   6.542%   $246.421   $246.42   $246.40   $246.40  
  Purchase #2 $231.41   11.196%   $257.3187   $257.32   $257.30   $257.30  
  Purchase #3 $95.96   5.752%   $101.4796   $101.48   $101.50   $101.50  
  Purchase #4 $206.34   3.233%   $213.011   $213.01   $213.00   $213.00  
  Purchase #5 $27.78   6.202%   $29.5029   $29.50   $29.50   $29.50  
  Purchase #6 $245.95   12.294%   $276.1871   $276.19   $276.20   $276.20  
  Purchase #7 $130.31   3.459%   $134.8174   $134.82   $134.80   $134.80  
  7 purchase totals = $1,169.04       $1,258.7377   $1,258.74   $1,258.70   $1,258.70