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	$31.69	4.486%	$33.1116	$33.11	$33.10	$33.10
Purchase #2	$26.73	5.797%	$28.2795	$28.28	$28.30	$28.30
Purchase #3	$248.56	8.450%	$269.5633	$269.56	$269.55	$269.60
Purchase #4	$240.69	7.575%	$258.9223	$258.92	$258.90	$258.90
Purchase #5	$140.76	7.833%	$151.7857	$151.79	$151.80	$151.80
Purchase #6	$99.79	6.735%	$106.5109	$106.51	$106.50	$106.50
Purchase #7	$200.34	13.479%	$227.3438	$227.34	$227.35	$227.30
7 purchase totals =	$988.56		$1,075.5171	$1,075.51	$1,075.50	$1,075.50