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	$89.33	11.168%	$99.3064	$99.31	$99.30	$99.30
Purchase #2	$240.72	7.468%	$258.697	$258.70	$258.70	$258.70
Purchase #3	$144.34	7.530%	$155.2088	$155.21	$155.20	$155.20
Purchase #4	$89.73	10.804%	$99.4244	$99.42	$99.40	$99.40
Purchase #5	$128.83	4.489%	$134.6132	$134.61	$134.60	$134.60
Purchase #6	$195.42	7.175%	$209.4414	$209.44	$209.45	$209.40
Purchase #7	$71.30	4.251%	$74.331	$74.33	$74.35	$74.30
7 purchase totals =	$959.67		$1,031.0222	$1,031.02	$1,031.00	$1,030.90