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 $246.98   8.412%   $267.756   $267.76   $267.75   $267.80  
  Purchase #2 $72.44   7.160%   $77.6267   $77.63   $77.65   $77.60  
  Purchase #3 $33.34   7.169%   $35.7301   $35.73   $35.75   $35.70  
  Purchase #4 $27.95   7.586%   $30.0703   $30.07   $30.05   $30.10  
  Purchase #5 $92.54   13.662%   $105.1828   $105.18   $105.20   $105.20  
  Purchase #6 $217.54   6.325%   $231.2994   $231.30   $231.30   $231.30  
  Purchase #7 $192.30   11.290%   $214.0107   $214.01   $214.00   $214.00  
  7 purchase totals = $883.09       $961.6760   $961.68   $961.70   $961.70