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	$125.67	11.343%	$139.9247	$139.92	$139.90	$139.90
Purchase #2	$65.68	3.188%	$67.7739	$67.77	$67.75	$67.80
Purchase #3	$73.42	9.727%	$80.5616	$80.56	$80.55	$80.60
Purchase #4	$49.78	7.400%	$53.4637	$53.46	$53.45	$53.50
Purchase #5	$142.57	4.814%	$149.4333	$149.43	$149.45	$149.40
Purchase #6	$159.38	8.451%	$172.8492	$172.85	$172.85	$172.80
Purchase #7	$42.77	5.643%	$45.1835	$45.18	$45.20	$45.20
7 purchase totals =	$659.27		$709.1899	$709.17	$709.15	$709.20