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	$123.41	3.341%	$127.5331	$127.53	$127.55	$127.50
Purchase #2	$196.82	13.618%	$223.6229	$223.62	$223.60	$223.60
Purchase #3	$63.68	12.527%	$71.6572	$71.66	$71.65	$71.70
Purchase #4	$125.27	9.278%	$136.8926	$136.89	$136.90	$136.90
Purchase #5	$185.49	4.333%	$193.5273	$193.53	$193.55	$193.50
Purchase #6	$93.33	6.717%	$99.599	$99.60	$99.60	$99.60
Purchase #7	$81.47	5.679%	$86.0967	$86.10	$86.10	$86.10
7 purchase totals =	$869.47		$938.9288	$938.93	$938.95	$938.90