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	$95.27	13.580%	$108.2077	$108.21	$108.20	$108.20
Purchase #2	$196.35	6.657%	$209.421	$209.42	$209.40	$209.40
Purchase #3	$127.43	4.809%	$133.5581	$133.56	$133.55	$133.60
Purchase #4	$53.49	11.659%	$59.7264	$59.73	$59.75	$59.70
Purchase #5	$99.51	4.613%	$104.1004	$104.10	$104.10	$104.10
Purchase #6	$115.37	7.169%	$123.6409	$123.64	$123.65	$123.60
Purchase #7	$51.41	7.699%	$55.3681	$55.37	$55.35	$55.40
7 purchase totals =	$738.83		$794.0226	$794.03	$794.00	$794.00