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 $172.76   6.804%   $184.5146   $184.51   $184.50   $184.50  
  Purchase #2 $84.76   13.379%   $96.1   $96.10   $96.10   $96.10  
  Purchase #3 $98.53   13.584%   $111.9143   $111.91   $111.90   $111.90  
  Purchase #4 $117.78   5.709%   $124.5041   $124.50   $124.50   $124.50  
  Purchase #5 $23.46   6.513%   $24.9879   $24.99   $25.00   $25.00  
  Purchase #6 $119.97   3.449%   $124.1078   $124.11   $124.10   $124.10  
  Purchase #7 $69.34   9.831%   $76.1568   $76.16   $76.15   $76.20  
  7 purchase totals = $686.60       $742.2855   $742.28   $742.25   $742.30