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	$99.90	3.501%	$103.3975	$103.40	$103.40	$103.40
Purchase #2	$163.54	4.540%	$170.9647	$170.96	$170.95	$171.00
Purchase #3	$58.87	13.710%	$66.9411	$66.94	$66.95	$66.90
Purchase #4	$169.25	8.400%	$183.467	$183.47	$183.45	$183.50
Purchase #5	$144.33	6.287%	$153.404	$153.40	$153.40	$153.40
Purchase #6	$232.52	10.453%	$256.8253	$256.83	$256.85	$256.80
Purchase #7	$146.76	8.612%	$159.399	$159.40	$159.40	$159.40
7 purchase totals =	$1,015.17		$1,094.3986	$1,094.40	$1,094.40	$1,094.40