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 $49.88   7.828%   $53.7846   $53.78   $53.80   $53.80  
  Purchase #2 $78.84   10.296%   $86.9574   $86.96   $86.95   $87.00  
  Purchase #3 $88.25   10.183%   $97.2365   $97.24   $97.25   $97.20  
  Purchase #4 $52.79   5.382%   $55.6312   $55.63   $55.65   $55.60  
  Purchase #5 $231.42   10.398%   $255.4831   $255.48   $255.50   $255.50  
  Purchase #6 $159.94   9.291%   $174.8   $174.80   $174.80   $174.80  
  Purchase #7 $215.30   3.106%   $221.9872   $221.99   $222.00   $222.00  
  7 purchase totals = $876.42       $945.8800   $945.88   $945.95   $945.90