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	$36.99	13.801%	$42.095	$42.10	$42.10	$42.10
Purchase #2	$88.95	6.491%	$94.7237	$94.72	$94.70	$94.70
Purchase #3	$50.40	7.578%	$54.2193	$54.22	$54.20	$54.20
Purchase #4	$173.49	6.650%	$185.0271	$185.03	$185.05	$185.00
Purchase #5	$64.93	5.235%	$68.3291	$68.33	$68.35	$68.30
Purchase #6	$80.87	12.871%	$91.2788	$91.28	$91.30	$91.30
Purchase #7	$120.27	6.224%	$127.7556	$127.76	$127.75	$127.80
7 purchase totals =	$615.90		$663.4286	$663.44	$663.45	$663.40