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	$89.41	11.363%	$99.5697	$99.57	$99.55	$99.60
Purchase #2	$202.32	3.418%	$209.2353	$209.24	$209.25	$209.20
Purchase #3	$145.74	13.676%	$165.6714	$165.67	$165.65	$165.70
Purchase #4	$50.40	4.669%	$52.7532	$52.75	$52.75	$52.80
Purchase #5	$163.72	5.636%	$172.9473	$172.95	$172.95	$172.90
Purchase #6	$40.73	6.249%	$43.2752	$43.28	$43.30	$43.30
Purchase #7	$100.55	8.290%	$108.8856	$108.89	$108.90	$108.90
7 purchase totals =	$792.87		$852.3377	$852.35	$852.35	$852.40