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	$67.33	6.749%	$71.8741	$71.87	$71.85	$71.90
Purchase #2	$156.97	13.504%	$178.1672	$178.17	$178.15	$178.20
Purchase #3	$172.25	4.840%	$180.5869	$180.59	$180.60	$180.60
Purchase #4	$240.69	4.364%	$251.1937	$251.19	$251.20	$251.20
Purchase #5	$136.94	4.561%	$143.1858	$143.19	$143.20	$143.20
Purchase #6	$42.64	5.389%	$44.9379	$44.94	$44.95	$44.90
Purchase #7	$113.27	12.789%	$127.7561	$127.76	$127.75	$127.80
7 purchase totals =	$930.09		$997.7017	$997.71	$997.70	$997.80