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	$34.64	11.317%	$38.5602	$38.56	$38.55	$38.60
Purchase #2	$62.46	8.248%	$67.6117	$67.61	$67.60	$67.60
Purchase #3	$139.69	5.396%	$147.2277	$147.23	$147.25	$147.20
Purchase #4	$46.49	7.562%	$50.0056	$50.01	$50.00	$50.00
Purchase #5	$85.73	3.287%	$88.5479	$88.55	$88.55	$88.50
Purchase #6	$134.30	13.130%	$151.9336	$151.93	$151.95	$151.90
Purchase #7	$159.65	7.747%	$172.0181	$172.02	$172.00	$172.00
7 purchase totals =	$662.96		$715.9048	$715.91	$715.90	$715.80