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	$155.89	7.239%	$167.1749	$167.17	$167.15	$167.20
Purchase #2	$175.82	11.679%	$196.354	$196.35	$196.35	$196.40
Purchase #3	$133.56	9.303%	$145.9851	$145.99	$146.00	$146.00
Purchase #4	$230.93	11.433%	$257.3322	$257.33	$257.35	$257.30
Purchase #5	$17.43	6.308%	$18.5295	$18.53	$18.55	$18.50
Purchase #6	$5.57	9.251%	$6.0853	$6.09	$6.10	$6.10
Purchase #7	$190.40	11.298%	$211.9114	$211.91	$211.90	$211.90
7 purchase totals =	$909.60		$1,003.3724	$1,003.37	$1,003.40	$1,003.40