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	$173.36	13.275%	$196.3735	$196.37	$196.35	$196.40
Purchase #2	$146.99	8.575%	$159.5944	$159.59	$159.60	$159.60
Purchase #3	$79.52	11.246%	$88.4628	$88.46	$88.45	$88.50
Purchase #4	$238.55	13.208%	$270.0577	$270.06	$270.05	$270.10
Purchase #5	$229.34	4.186%	$238.9402	$238.94	$238.95	$238.90
Purchase #6	$134.51	5.435%	$141.8206	$141.82	$141.80	$141.80
Purchase #7	$120.41	13.428%	$136.5787	$136.58	$136.60	$136.60
7 purchase totals =	$1,122.68		$1,231.8279	$1,231.82	$1,231.80	$1,231.90