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	$243.55	8.676%	$264.6804	$264.68	$264.70	$264.70
Purchase #2	$126.50	9.473%	$138.4833	$138.48	$138.50	$138.50
Purchase #3	$10.25	6.396%	$10.9056	$10.91	$10.90	$10.90
Purchase #4	$199.27	11.693%	$222.5706	$222.57	$222.55	$222.60
Purchase #5	$113.66	8.735%	$123.5882	$123.59	$123.60	$123.60
Purchase #6	$145.43	4.292%	$151.6719	$151.67	$151.65	$151.70
Purchase #7	$202.80	3.307%	$209.5066	$209.51	$209.50	$209.50
7 purchase totals =	$1,041.46		$1,121.4066	$1,121.41	$1,121.40	$1,121.50