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 $86.39   7.380%   $92.7656   $92.77   $92.75   $92.80  
  Purchase #2 $98.41   10.645%   $108.8857   $108.89   $108.90   $108.90  
  Purchase #3 $194.47   10.545%   $214.9769   $214.98   $215.00   $215.00  
  Purchase #4 $147.76   13.183%   $167.2392   $167.24   $167.25   $167.20  
  Purchase #5 $27.64   6.593%   $29.4623   $29.46   $29.45   $29.50  
  Purchase #6 $16.51   9.812%   $18.13   $18.13   $18.15   $18.10  
  Purchase #7 $113.65   9.535%   $124.4865   $124.49   $124.50   $124.50  
  7 purchase totals = $684.83       $755.9462   $755.96   $756.00   $756.00