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	$99.54	12.216%	$111.6998	$111.70	$111.70	$111.70
Purchase #2	$54.53	4.185%	$56.8121	$56.81	$56.80	$56.80
Purchase #3	$93.76	10.735%	$103.8251	$103.83	$103.85	$103.80
Purchase #4	$134.89	8.394%	$146.2127	$146.21	$146.20	$146.20
Purchase #5	$122.51	8.158%	$132.5044	$132.50	$132.50	$132.50
Purchase #6	$220.54	13.137%	$249.5123	$249.51	$249.50	$249.50
Purchase #7	$167.80	10.379%	$185.216	$185.22	$185.20	$185.20
7 purchase totals =	$893.57		$985.7824	$985.78	$985.75	$985.70