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	$228.25	13.198%	$258.3744	$258.37	$258.35	$258.40
Purchase #2	$53.39	11.534%	$59.548	$59.55	$59.55	$59.50
Purchase #3	$88.37	10.653%	$97.7841	$97.78	$97.80	$97.80
Purchase #4	$187.91	11.257%	$209.063	$209.06	$209.05	$209.10
Purchase #5	$29.30	4.478%	$30.6121	$30.61	$30.60	$30.60
Purchase #6	$156.31	10.258%	$172.3443	$172.34	$172.35	$172.30
Purchase #7	$147.31	12.185%	$165.2597	$165.26	$165.25	$165.30
7 purchase totals =	$890.84		$992.9856	$992.97	$992.95	$993.00