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	$6.80	11.152%	$7.5583	$7.56	$7.55	$7.60
Purchase #2	$118.43	7.440%	$127.2412	$127.24	$127.25	$127.20
Purchase #3	$69.52	3.248%	$71.778	$71.78	$71.80	$71.80
Purchase #4	$205.76	12.834%	$232.1672	$232.17	$232.15	$232.20
Purchase #5	$206.63	6.731%	$220.5383	$220.54	$220.55	$220.50
Purchase #6	$151.40	10.133%	$166.7414	$166.74	$166.75	$166.70
Purchase #7	$14.54	6.818%	$15.5313	$15.53	$15.55	$15.50
7 purchase totals =	$773.08		$841.5557	$841.56	$841.60	$841.50