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	$243.38	6.329%	$258.7835	$258.78	$258.80	$258.80
Purchase #2	$174.61	9.694%	$191.5367	$191.54	$191.55	$191.50
Purchase #3	$169.73	9.272%	$185.4674	$185.47	$185.45	$185.50
Purchase #4	$12.55	13.567%	$14.2527	$14.25	$14.25	$14.30
Purchase #5	$245.28	4.389%	$256.0453	$256.05	$256.05	$256.00
Purchase #6	$203.89	5.691%	$215.4934	$215.49	$215.50	$215.50
Purchase #7	$73.51	7.348%	$78.9115	$78.91	$78.90	$78.90
7 purchase totals =	$1,122.95		$1,200.4905	$1,200.49	$1,200.50	$1,200.50