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 $208.55   11.133%   $231.7679   $231.77   $231.75   $231.80  
  Purchase #2 $160.63   3.615%   $166.4368   $166.44   $166.45   $166.40  
  Purchase #3 $222.49   8.397%   $241.1725   $241.17   $241.15   $241.20  
  Purchase #4 $137.94   8.365%   $149.4787   $149.48   $149.50   $149.50  
  Purchase #5 $10.25   4.280%   $10.6887   $10.69   $10.70   $10.70  
  Purchase #6 $82.95   13.847%   $94.4361   $94.44   $94.45   $94.40  
  Purchase #7 $70.36   5.211%   $74.0265   $74.03   $74.05   $74.00  
  7 purchase totals = $893.17       $968.0072   $968.02   $968.05   $968.00