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	$97.64	11.747%	$109.1098	$109.11	$109.10	$109.10
Purchase #2	$30.32	8.386%	$32.8626	$32.86	$32.85	$32.90
Purchase #3	$143.85	9.368%	$157.3259	$157.33	$157.35	$157.30
Purchase #4	$14.61	12.446%	$16.4284	$16.43	$16.45	$16.40
Purchase #5	$216.59	7.588%	$233.0248	$233.02	$233.00	$233.00
Purchase #6	$40.95	4.793%	$42.9127	$42.91	$42.90	$42.90
Purchase #7	$33.99	13.286%	$38.5059	$38.51	$38.50	$38.50
7 purchase totals =	$577.95		$630.1701	$630.17	$630.15	$630.10