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	$209.99	6.647%	$223.948	$223.95	$223.95	$223.90
Purchase #2	$247.97	7.488%	$266.538	$266.54	$266.55	$266.50
Purchase #3	$135.27	11.792%	$151.221	$151.22	$151.20	$151.20
Purchase #4	$161.38	4.116%	$168.0224	$168.02	$168.00	$168.00
Purchase #5	$107.37	12.168%	$120.4348	$120.43	$120.45	$120.40
Purchase #6	$140.65	4.410%	$146.8527	$146.85	$146.85	$146.90
Purchase #7	$155.89	3.491%	$161.3321	$161.33	$161.35	$161.30
7 purchase totals =	$1,158.52		$1,238.3490	$1,238.34	$1,238.35	$1,238.20