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	$80.66	11.519%	$89.9512	$89.95	$89.95	$90.00
Purchase #2	$20.88	13.457%	$23.6898	$23.69	$23.70	$23.70
Purchase #3	$26.69	9.308%	$29.1743	$29.17	$29.15	$29.20
Purchase #4	$174.98	5.810%	$185.1463	$185.15	$185.15	$185.10
Purchase #5	$33.67	13.774%	$38.3077	$38.31	$38.30	$38.30
Purchase #6	$36.80	12.663%	$41.46	$41.46	$41.45	$41.50
Purchase #7	$69.82	6.410%	$74.2955	$74.30	$74.30	$74.30
7 purchase totals =	$443.50		$482.0248	$482.03	$482.00	$482.10