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	$75.61	3.529%	$78.2783	$78.28	$78.30	$78.30
Purchase #2	$82.79	7.241%	$88.7848	$88.78	$88.80	$88.80
Purchase #3	$37.57	13.823%	$42.7633	$42.76	$42.75	$42.80
Purchase #4	$36.31	3.149%	$37.4534	$37.45	$37.45	$37.50
Purchase #5	$145.55	10.652%	$161.054	$161.05	$161.05	$161.10
Purchase #6	$35.83	9.102%	$39.0912	$39.09	$39.10	$39.10
Purchase #7	$55.53	3.528%	$57.4891	$57.49	$57.50	$57.50
7 purchase totals =	$469.19		$504.9141	$504.90	$504.95	$505.10