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	$29.25	12.585%	$32.9311	$32.93	$32.95	$32.90
Purchase #2	$148.89	11.213%	$165.585	$165.59	$165.60	$165.60
Purchase #3	$70.54	7.430%	$75.7811	$75.78	$75.80	$75.80
Purchase #4	$85.81	5.687%	$90.69	$90.69	$90.70	$90.70
Purchase #5	$224.78	7.778%	$242.2634	$242.26	$242.25	$242.30
Purchase #6	$71.63	8.169%	$77.4815	$77.48	$77.50	$77.50
Purchase #7	$203.58	12.382%	$228.7873	$228.79	$228.80	$228.80
7 purchase totals =	$834.48		$913.5194	$913.52	$913.60	$913.60