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	$112.47	7.130%	$120.4891	$120.49	$120.50	$120.50
Purchase #2	$231.48	13.516%	$262.7668	$262.77	$262.75	$262.80
Purchase #3	$71.62	4.208%	$74.6338	$74.63	$74.65	$74.60
Purchase #4	$84.77	13.124%	$95.8952	$95.90	$95.90	$95.90
Purchase #5	$38.41	6.461%	$40.8917	$40.89	$40.90	$40.90
Purchase #6	$45.40	13.345%	$51.4586	$51.46	$51.45	$51.50
Purchase #7	$129.57	13.777%	$147.4209	$147.42	$147.40	$147.40
7 purchase totals =	$713.72		$793.5561	$793.56	$793.55	$793.60