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	$39.57	3.400%	$40.9154	$40.92	$40.90	$40.90
Purchase #2	$208.95	6.613%	$222.7679	$222.77	$222.75	$222.80
Purchase #3	$190.94	4.378%	$199.2994	$199.30	$199.30	$199.30
Purchase #4	$71.90	8.399%	$77.9389	$77.94	$77.95	$77.90
Purchase #5	$32.61	7.795%	$35.1519	$35.15	$35.15	$35.20
Purchase #6	$141.69	11.342%	$157.7605	$157.76	$157.75	$157.80
Purchase #7	$53.39	13.489%	$60.5918	$60.59	$60.60	$60.60
7 purchase totals =	$739.05		$794.4258	$794.43	$794.40	$794.50