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 $49.63   5.233%   $52.2271   $52.23   $52.25   $52.20  
  Purchase #2 $207.52   4.752%   $217.3814   $217.38   $217.40   $217.40  
  Purchase #3 $156.86   4.342%   $163.6709   $163.67   $163.65   $163.70  
  Purchase #4 $206.82   6.166%   $219.5725   $219.57   $219.55   $219.60  
  Purchase #5 $34.27   11.556%   $38.2302   $38.23   $38.25   $38.20  
  Purchase #6 $75.46   8.239%   $81.6771   $81.68   $81.70   $81.70  
  Purchase #7 $88.63   6.605%   $94.484   $94.48   $94.50   $94.50  
  7 purchase totals = $819.19       $867.2432   $867.24   $867.30   $867.30