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	$119.75	13.744%	$136.2084	$136.21	$136.20	$136.20
Purchase #2	$82.62	9.140%	$90.1715	$90.17	$90.15	$90.20
Purchase #3	$137.38	12.316%	$154.2997	$154.30	$154.30	$154.30
Purchase #4	$73.31	10.341%	$80.891	$80.89	$80.90	$80.90
Purchase #5	$60.59	8.642%	$65.8262	$65.83	$65.85	$65.80
Purchase #6	$98.42	6.337%	$104.6569	$104.66	$104.65	$104.70
Purchase #7	$240.36	9.150%	$262.3529	$262.35	$262.35	$262.40
7 purchase totals =	$812.43		$894.4066	$894.41	$894.40	$894.50