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	$22.38	11.852%	$25.0325	$25.03	$25.05	$25.00
Purchase #2	$73.55	13.554%	$83.519	$83.52	$83.50	$83.50
Purchase #3	$131.54	4.689%	$137.7079	$137.71	$137.70	$137.70
Purchase #4	$61.77	5.473%	$65.1507	$65.15	$65.15	$65.20
Purchase #5	$117.37	11.670%	$131.0671	$131.07	$131.05	$131.10
Purchase #6	$13.79	7.499%	$14.8241	$14.82	$14.80	$14.80
Purchase #7	$49.37	12.216%	$55.401	$55.40	$55.40	$55.40
7 purchase totals =	$469.77		$512.7023	$512.70	$512.65	$512.70