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 $84.83   12.673%   $95.5805   $95.58   $95.60   $95.60  
  Purchase #2 $16.63   4.816%   $17.4309   $17.43   $17.45   $17.40  
  Purchase #3 $177.82   4.290%   $185.4485   $185.45   $185.45   $185.40  
  Purchase #4 $101.46   11.507%   $113.135   $113.14   $113.15   $113.10  
  Purchase #5 $6.42   8.706%   $6.9789   $6.98   $7.00   $7.00  
  Purchase #6 $145.26   6.362%   $154.5014   $154.50   $154.50   $154.50  
  Purchase #7 $191.92   9.680%   $210.4979   $210.50   $210.50   $210.50  
  7 purchase totals = $724.34       $783.5731   $783.58   $783.65   $783.50