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	$79.33	12.251%	$89.0487	$89.05	$89.05	$89.00
Purchase #2	$172.37	8.836%	$187.6006	$187.60	$187.60	$187.60
Purchase #3	$139.90	6.726%	$149.3097	$149.31	$149.30	$149.30
Purchase #4	$169.73	11.562%	$189.3542	$189.35	$189.35	$189.40
Purchase #5	$188.54	4.262%	$196.5756	$196.58	$196.60	$196.60
Purchase #6	$153.55	13.148%	$173.7388	$173.74	$173.75	$173.70
Purchase #7	$13.89	8.131%	$15.0194	$15.02	$15.00	$15.00
7 purchase totals =	$917.31		$1,000.6470	$1,000.65	$1,000.65	$1,000.60