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	$40.88	11.852%	$45.7251	$45.73	$45.75	$45.70
Purchase #2	$173.38	6.707%	$185.0086	$185.01	$185.00	$185.00
Purchase #3	$162.76	10.173%	$179.3176	$179.32	$179.30	$179.30
Purchase #4	$37.51	11.816%	$41.9422	$41.94	$41.95	$41.90
Purchase #5	$67.79	9.722%	$74.3805	$74.38	$74.40	$74.40
Purchase #6	$60.91	13.561%	$69.17	$69.17	$69.15	$69.20
Purchase #7	$70.59	6.108%	$74.9016	$74.90	$74.90	$74.90
7 purchase totals =	$613.82		$670.4456	$670.45	$670.45	$670.40