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	$72.27	8.128%	$78.1441	$78.14	$78.15	$78.10
Purchase #2	$161.75	3.545%	$167.484	$167.48	$167.50	$167.50
Purchase #3	$160.27	7.206%	$171.8191	$171.82	$171.80	$171.80
Purchase #4	$16.52	9.168%	$18.0346	$18.03	$18.05	$18.00
Purchase #5	$147.62	8.207%	$159.7352	$159.74	$159.75	$159.70
Purchase #6	$83.75	6.465%	$89.1644	$89.16	$89.15	$89.20
Purchase #7	$92.43	7.777%	$99.6183	$99.62	$99.60	$99.60
7 purchase totals =	$734.61		$783.9997	$783.99	$784.00	$783.90