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	$183.27	13.158%	$207.3847	$207.38	$207.40	$207.40
Purchase #2	$47.87	11.774%	$53.5062	$53.51	$53.50	$53.50
Purchase #3	$135.72	12.123%	$152.1733	$152.17	$152.15	$152.20
Purchase #4	$6.80	13.290%	$7.7037	$7.70	$7.70	$7.70
Purchase #5	$40.43	7.742%	$43.5601	$43.56	$43.55	$43.60
Purchase #6	$64.63	13.831%	$73.569	$73.57	$73.55	$73.60
Purchase #7	$50.89	6.692%	$54.2956	$54.30	$54.30	$54.30
7 purchase totals =	$529.61		$592.1926	$592.19	$592.15	$592.30