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	$13.40	5.684%	$14.1617	$14.16	$14.15	$14.20
Purchase #2	$145.89	9.282%	$159.4315	$159.43	$159.45	$159.40
Purchase #3	$114.77	9.182%	$125.3082	$125.31	$125.30	$125.30
Purchase #4	$6.47	4.721%	$6.7754	$6.78	$6.80	$6.80
Purchase #5	$80.43	7.407%	$86.3875	$86.39	$86.40	$86.40
Purchase #6	$59.76	11.522%	$66.6455	$66.65	$66.65	$66.60
Purchase #7	$66.93	9.861%	$73.53	$73.53	$73.55	$73.50
7 purchase totals =	$487.65		$532.2398	$532.25	$532.30	$532.20