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	$89.39	11.274%	$99.4678	$99.47	$99.45	$99.50
Purchase #2	$155.91	3.562%	$161.4635	$161.46	$161.45	$161.50
Purchase #3	$31.60	13.577%	$35.8903	$35.89	$35.90	$35.90
Purchase #4	$214.84	7.719%	$231.4235	$231.42	$231.40	$231.40
Purchase #5	$59.95	8.265%	$64.9049	$64.90	$64.90	$64.90
Purchase #6	$150.55	4.453%	$157.254	$157.25	$157.25	$157.30
Purchase #7	$175.43	7.567%	$188.7048	$188.70	$188.70	$188.70
7 purchase totals =	$877.67		$939.1088	$939.09	$939.05	$939.20