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	$118.68	7.196%	$127.2202	$127.22	$127.20	$127.20
Purchase #2	$152.42	11.723%	$170.2882	$170.29	$170.30	$170.30
Purchase #3	$200.58	4.449%	$209.5038	$209.50	$209.50	$209.50
Purchase #4	$28.29	8.300%	$30.6381	$30.64	$30.65	$30.60
Purchase #5	$79.55	12.864%	$89.7833	$89.78	$89.80	$89.80
Purchase #6	$114.52	8.728%	$124.5153	$124.52	$124.50	$124.50
Purchase #7	$96.76	11.234%	$107.63	$107.63	$107.65	$107.60
7 purchase totals =	$790.80		$859.5789	$859.58	$859.60	$859.50