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	$40.70	3.432%	$42.0968	$42.10	$42.10	$42.10
Purchase #2	$59.28	11.147%	$65.8879	$65.89	$65.90	$65.90
Purchase #3	$167.95	10.339%	$185.3144	$185.31	$185.30	$185.30
Purchase #4	$42.52	12.265%	$47.7351	$47.74	$47.75	$47.70
Purchase #5	$119.52	9.547%	$130.9306	$130.93	$130.95	$130.90
Purchase #6	$130.26	10.652%	$144.1353	$144.14	$144.15	$144.10
Purchase #7	$52.53	8.735%	$57.1185	$57.12	$57.10	$57.10
7 purchase totals =	$612.76		$673.2186	$673.23	$673.25	$673.10