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 $243.48   9.475%   $266.5497   $266.55   $266.55   $266.50  
  Purchase #2 $79.87   8.478%   $86.6414   $86.64   $86.65   $86.60  
  Purchase #3 $100.81   10.207%   $111.0997   $111.10   $111.10   $111.10  
  Purchase #4 $229.26   6.532%   $244.2353   $244.24   $244.25   $244.20  
  Purchase #5 $48.90   10.750%   $54.1568   $54.16   $54.15   $54.20  
  Purchase #6 $86.94   9.386%   $95.1002   $95.10   $95.10   $95.10  
  Purchase #7 $221.63   7.214%   $237.6184   $237.62   $237.60   $237.60  
  7 purchase totals = $1,010.89       $1,095.4015   $1,095.41   $1,095.40   $1,095.30