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	$115.94	13.825%	$131.9687	$131.97	$131.95	$132.00
Purchase #2	$250.54	12.120%	$280.9054	$280.91	$280.90	$280.90
Purchase #3	$14.27	5.779%	$15.0947	$15.09	$15.10	$15.10
Purchase #4	$37.83	6.794%	$40.4002	$40.40	$40.40	$40.40
Purchase #5	$56.99	6.197%	$60.5217	$60.52	$60.50	$60.50
Purchase #6	$42.32	7.530%	$45.5067	$45.51	$45.50	$45.50
Purchase #7	$223.54	12.181%	$250.7694	$250.77	$250.75	$250.80
7 purchase totals =	$741.43		$825.1668	$825.17	$825.10	$825.20