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	$127.55	4.576%	$133.3867	$133.39	$133.40	$133.40
Purchase #2	$69.32	13.364%	$78.5839	$78.58	$78.60	$78.60
Purchase #3	$20.59	9.292%	$22.5032	$22.50	$22.50	$22.50
Purchase #4	$72.31	12.171%	$81.1109	$81.11	$81.10	$81.10
Purchase #5	$36.52	9.222%	$39.8879	$39.89	$39.90	$39.90
Purchase #6	$142.72	10.388%	$157.5458	$157.55	$157.55	$157.50
Purchase #7	$250.86	9.825%	$275.507	$275.51	$275.50	$275.50
7 purchase totals =	$719.87		$788.5254	$788.53	$788.55	$788.50