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	$10.25	12.602%	$11.5417	$11.54	$11.55	$11.50
Purchase #2	$91.34	12.657%	$102.9009	$102.90	$102.90	$102.90
Purchase #3	$214.31	4.494%	$223.9411	$223.94	$223.95	$223.90
Purchase #4	$32.97	13.384%	$37.3827	$37.38	$37.40	$37.40
Purchase #5	$120.38	12.287%	$135.1711	$135.17	$135.15	$135.20
Purchase #6	$173.67	9.794%	$190.6792	$190.68	$190.70	$190.70
Purchase #7	$49.31	3.199%	$50.8874	$50.89	$50.90	$50.90
7 purchase totals =	$692.23		$752.5041	$752.50	$752.55	$752.50