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 $72.58   5.564%   $76.6184   $76.62   $76.60   $76.60  
  Purchase #2 $151.41   11.519%   $168.8509   $168.85   $168.85   $168.90  
  Purchase #3 $58.51   12.206%   $65.6517   $65.65   $65.65   $65.70  
  Purchase #4 $112.80   11.471%   $125.7393   $125.74   $125.75   $125.70  
  Purchase #5 $173.94   10.411%   $192.0489   $192.05   $192.05   $192.00  
  Purchase #6 $126.73   8.619%   $137.6529   $137.65   $137.65   $137.70  
  Purchase #7 $143.97   4.468%   $150.4026   $150.40   $150.40   $150.40  
  7 purchase totals = $839.94       $916.9647   $916.96   $916.95   $917.00