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	$19.71	7.510%	$21.1902	$21.19	$21.20	$21.20
Purchase #2	$114.55	12.127%	$128.4415	$128.44	$128.45	$128.40
Purchase #3	$78.53	3.170%	$81.0194	$81.02	$81.00	$81.00
Purchase #4	$47.52	5.535%	$50.1502	$50.15	$50.15	$50.20
Purchase #5	$148.41	11.278%	$165.1477	$165.15	$165.15	$165.10
Purchase #6	$136.41	4.149%	$142.0697	$142.07	$142.05	$142.10
Purchase #7	$131.60	11.385%	$146.5827	$146.58	$146.60	$146.60
7 purchase totals =	$676.73		$734.6014	$734.60	$734.60	$734.60