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	$29.47	11.732%	$32.9274	$32.93	$32.95	$32.90
Purchase #2	$85.78	4.471%	$89.6152	$89.62	$89.60	$89.60
Purchase #3	$43.55	13.126%	$49.2664	$49.27	$49.25	$49.30
Purchase #4	$138.82	5.420%	$146.344	$146.34	$146.35	$146.30
Purchase #5	$236.28	5.644%	$249.6156	$249.62	$249.60	$249.60
Purchase #6	$70.78	12.311%	$79.4937	$79.49	$79.50	$79.50
Purchase #7	$133.96	8.625%	$145.5141	$145.51	$145.50	$145.50
7 purchase totals =	$738.64		$792.7764	$792.78	$792.75	$792.70