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	$154.64	11.174%	$171.9195	$171.92	$171.90	$171.90
Purchase #2	$135.58	5.477%	$143.0057	$143.01	$143.00	$143.00
Purchase #3	$221.40	7.567%	$238.1533	$238.15	$238.15	$238.20
Purchase #4	$69.30	13.307%	$78.5218	$78.52	$78.50	$78.50
Purchase #5	$88.44	12.556%	$99.5445	$99.54	$99.55	$99.50
Purchase #6	$213.78	11.411%	$238.1744	$238.17	$238.15	$238.20
Purchase #7	$237.30	6.559%	$252.8645	$252.86	$252.85	$252.90
7 purchase totals =	$1,120.44		$1,222.1837	$1,222.17	$1,222.10	$1,222.20