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	$171.88	4.188%	$179.0783	$179.08	$179.10	$179.10
Purchase #2	$45.89	7.119%	$49.1569	$49.16	$49.15	$49.20
Purchase #3	$29.25	3.862%	$30.3796	$30.38	$30.40	$30.40
Purchase #4	$71.27	10.543%	$78.784	$78.78	$78.80	$78.80
Purchase #5	$130.73	11.124%	$145.2724	$145.27	$145.25	$145.30
Purchase #6	$92.57	10.558%	$102.3435	$102.34	$102.35	$102.30
Purchase #7	$231.49	10.842%	$256.5881	$256.59	$256.60	$256.60
7 purchase totals =	$773.08		$841.6028	$841.60	$841.65	$841.70