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 $247.58   8.873%   $269.5478   $269.55   $269.55   $269.50  
  Purchase #2 $124.68   13.267%   $141.2213   $141.22   $141.20   $141.20  
  Purchase #3 $231.48   5.511%   $244.2369   $244.24   $244.25   $244.20  
  Purchase #4 $94.49   4.542%   $98.7817   $98.78   $98.80   $98.80  
  Purchase #5 $21.68   10.492%   $23.9547   $23.95   $23.95   $24.00  
  Purchase #6 $59.43   3.171%   $61.3145   $61.31   $61.30   $61.30  
  Purchase #7 $51.27   10.583%   $56.6959   $56.70   $56.70   $56.70  
  7 purchase totals = $830.61       $895.7528   $895.75   $895.75   $895.70