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	$194.44	12.220%	$218.2006	$218.20	$218.20	$218.20
Purchase #2	$237.86	11.167%	$264.4218	$264.42	$264.40	$264.40
Purchase #3	$48.91	3.535%	$50.639	$50.64	$50.65	$50.60
Purchase #4	$78.49	6.811%	$83.836	$83.84	$83.85	$83.80
Purchase #5	$214.76	4.122%	$223.6124	$223.61	$223.60	$223.60
Purchase #6	$232.48	13.637%	$264.1833	$264.18	$264.20	$264.20
Purchase #7	$161.78	8.708%	$175.8678	$175.87	$175.85	$175.90
7 purchase totals =	$1,168.72		$1,280.7609	$1,280.76	$1,280.75	$1,280.70