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 $60.63   10.816%   $67.1877   $67.19   $67.20   $67.20  
  Purchase #2 $197.48   12.835%   $222.8266   $222.83   $222.85   $222.80  
  Purchase #3 $106.64   8.157%   $115.3386   $115.34   $115.35   $115.30  
  Purchase #4 $217.53   8.801%   $236.6748   $236.67   $236.65   $236.70  
  Purchase #5 $62.49   7.201%   $66.9899   $66.99   $67.00   $67.00  
  Purchase #6 $70.86   5.253%   $74.5823   $74.58   $74.60   $74.60  
  Purchase #7 $166.63   6.824%   $178.0008   $178.00   $178.00   $178.00  
  7 purchase totals = $882.26       $961.6007   $961.60   $961.65   $961.60