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 $86.43   10.548%   $95.5466   $95.55   $95.55   $95.50  
  Purchase #2 $87.76   5.639%   $92.7088   $92.71   $92.70   $92.70  
  Purchase #3 $156.60   6.644%   $167.0045   $167.00   $167.00   $167.00  
  Purchase #4 $92.63   4.649%   $96.9364   $96.94   $96.95   $96.90  
  Purchase #5 $151.81   7.388%   $163.0257   $163.03   $163.05   $163.00  
  Purchase #6 $19.32   9.749%   $21.2035   $21.20   $21.20   $21.20  
  Purchase #7 $93.88   12.477%   $105.5934   $105.59   $105.60   $105.60  
  7 purchase totals = $688.43       $742.0189   $742.02   $742.05   $741.90