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	$28.50	10.569%	$31.5122	$31.51	$31.50	$31.50
Purchase #2	$140.73	8.332%	$152.4556	$152.46	$152.45	$152.50
Purchase #3	$17.93	6.120%	$19.0273	$19.03	$19.05	$19.00
Purchase #4	$12.93	12.575%	$14.5559	$14.56	$14.55	$14.60
Purchase #5	$121.25	5.397%	$127.7939	$127.79	$127.80	$127.80
Purchase #6	$131.31	13.812%	$149.4465	$149.45	$149.45	$149.40
Purchase #7	$99.35	10.364%	$109.6466	$109.65	$109.65	$109.60
7 purchase totals =	$552.00		$604.4380	$604.45	$604.45	$604.40