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 $48.41   5.667%   $51.1534   $51.15   $51.15   $51.20  
  Purchase #2 $179.75   8.649%   $195.2966   $195.30   $195.30   $195.30  
  Purchase #3 $111.62   4.606%   $116.7612   $116.76   $116.75   $116.80  
  Purchase #4 $52.33   7.106%   $56.0486   $56.05   $56.05   $56.00  
  Purchase #5 $15.65   6.110%   $16.6062   $16.61   $16.60   $16.60  
  Purchase #6 $39.29   9.178%   $42.896   $42.90   $42.90   $42.90  
  Purchase #7 $246.91   4.284%   $257.4876   $257.49   $257.50   $257.50  
  7 purchase totals = $693.96       $736.2496   $736.26   $736.25   $736.30