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	$164.84	4.103%	$171.6034	$171.60	$171.60	$171.60
Purchase #2	$158.63	13.232%	$179.6199	$179.62	$179.60	$179.60
Purchase #3	$48.42	6.449%	$51.5426	$51.54	$51.55	$51.50
Purchase #4	$31.82	11.836%	$35.5862	$35.59	$35.60	$35.60
Purchase #5	$100.31	7.560%	$107.8934	$107.89	$107.90	$107.90
Purchase #6	$233.94	12.608%	$263.4352	$263.44	$263.45	$263.40
Purchase #7	$36.76	9.812%	$40.3669	$40.37	$40.35	$40.40
7 purchase totals =	$774.72		$850.0476	$850.05	$850.05	$850.00