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	$226.99	8.150%	$245.4897	$245.49	$245.50	$245.50
Purchase #2	$111.83	4.469%	$116.8277	$116.83	$116.85	$116.80
Purchase #3	$115.54	12.609%	$130.1084	$130.11	$130.10	$130.10
Purchase #4	$102.95	9.103%	$112.3215	$112.32	$112.30	$112.30
Purchase #5	$100.98	3.434%	$104.4477	$104.45	$104.45	$104.40
Purchase #6	$95.97	6.526%	$102.233	$102.23	$102.25	$102.20
Purchase #7	$37.75	8.306%	$40.8855	$40.89	$40.90	$40.90
7 purchase totals =	$792.01		$852.3135	$852.32	$852.35	$852.20