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	$232.43	4.498%	$242.8847	$242.88	$242.90	$242.90
Purchase #2	$111.61	10.739%	$123.5958	$123.60	$123.60	$123.60
Purchase #3	$130.92	11.414%	$145.8632	$145.86	$145.85	$145.90
Purchase #4	$218.62	11.742%	$244.2904	$244.29	$244.30	$244.30
Purchase #5	$184.97	5.635%	$195.3931	$195.39	$195.40	$195.40
Purchase #6	$228.39	11.728%	$255.1756	$255.18	$255.20	$255.20
Purchase #7	$246.44	11.781%	$275.4731	$275.47	$275.45	$275.50
7 purchase totals =	$1,353.38		$1,482.6759	$1,482.67	$1,482.70	$1,482.80