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	$64.86	12.310%	$72.8443	$72.84	$72.85	$72.80
Purchase #2	$153.55	8.209%	$166.1549	$166.15	$166.15	$166.20
Purchase #3	$75.50	4.259%	$78.7155	$78.72	$78.70	$78.70
Purchase #4	$127.84	9.787%	$140.3517	$140.35	$140.35	$140.40
Purchase #5	$109.54	13.772%	$124.6258	$124.63	$124.65	$124.60
Purchase #6	$216.50	9.253%	$236.5327	$236.53	$236.55	$236.50
Purchase #7	$68.69	12.823%	$77.4981	$77.50	$77.50	$77.50
7 purchase totals =	$816.48		$896.7230	$896.72	$896.75	$896.70