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	$171.39	10.492%	$189.3722	$189.37	$189.35	$189.40
Purchase #2	$203.72	5.154%	$214.2197	$214.22	$214.20	$214.20
Purchase #3	$72.90	12.752%	$82.1962	$82.20	$82.20	$82.20
Purchase #4	$67.66	12.370%	$76.0295	$76.03	$76.05	$76.00
Purchase #5	$105.96	11.792%	$118.4548	$118.45	$118.45	$118.50
Purchase #6	$227.31	6.627%	$242.3738	$242.37	$242.35	$242.40
Purchase #7	$143.73	10.757%	$159.191	$159.19	$159.20	$159.20
7 purchase totals =	$992.67		$1,081.8372	$1,081.83	$1,081.80	$1,081.90