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	$223.65	11.860%	$250.1749	$250.17	$250.15	$250.20
Purchase #2	$31.50	4.540%	$32.9301	$32.93	$32.95	$32.90
Purchase #3	$46.39	4.404%	$48.433	$48.43	$48.45	$48.40
Purchase #4	$175.92	9.171%	$192.0536	$192.05	$192.05	$192.10
Purchase #5	$49.99	10.864%	$55.4209	$55.42	$55.40	$55.40
Purchase #6	$70.94	9.811%	$77.8999	$77.90	$77.90	$77.90
Purchase #7	$209.40	11.683%	$233.8642	$233.86	$233.85	$233.90
7 purchase totals =	$807.79		$890.7766	$890.76	$890.75	$890.80