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 $62.64   11.716%   $69.9789   $69.98   $70.00   $70.00  
  Purchase #2 $232.41   13.106%   $262.8697   $262.87   $262.85   $262.90  
  Purchase #3 $68.42   4.168%   $71.2717   $71.27   $71.25   $71.30  
  Purchase #4 $96.63   4.193%   $100.6817   $100.68   $100.70   $100.70  
  Purchase #5 $208.97   11.380%   $232.7508   $232.75   $232.75   $232.80  
  Purchase #6 $11.73   9.445%   $12.8379   $12.84   $12.85   $12.80  
  Purchase #7 $236.82   9.491%   $259.2966   $259.30   $259.30   $259.30  
  7 purchase totals = $917.62       $1,009.6873   $1,009.69   $1,009.70   $1,009.80