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	$66.83	6.432%	$71.1285	$71.13	$71.15	$71.10
Purchase #2	$113.49	12.538%	$127.7194	$127.72	$127.70	$127.70
Purchase #3	$175.94	8.659%	$191.1746	$191.17	$191.15	$191.20
Purchase #4	$151.29	3.390%	$156.4187	$156.42	$156.40	$156.40
Purchase #5	$134.65	5.821%	$142.488	$142.49	$142.50	$142.50
Purchase #6	$54.87	8.757%	$59.675	$59.68	$59.70	$59.70
Purchase #7	$61.45	4.402%	$64.155	$64.16	$64.15	$64.20
7 purchase totals =	$758.52		$812.7592	$812.77	$812.75	$812.80