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	$48.29	5.150%	$50.7769	$50.78	$50.80	$50.80
Purchase #2	$231.98	6.697%	$247.5157	$247.52	$247.50	$247.50
Purchase #3	$165.89	12.511%	$186.6445	$186.64	$186.65	$186.60
Purchase #4	$142.54	13.217%	$161.3795	$161.38	$161.40	$161.40
Purchase #5	$133.49	4.468%	$139.4543	$139.45	$139.45	$139.50
Purchase #6	$109.42	10.504%	$120.9135	$120.91	$120.90	$120.90
Purchase #7	$97.75	6.139%	$103.7509	$103.75	$103.75	$103.80
7 purchase totals =	$929.36		$1,010.4353	$1,010.43	$1,010.45	$1,010.50