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	$143.37	5.703%	$151.5464	$151.55	$151.55	$151.50
Purchase #2	$158.46	12.626%	$178.4672	$178.47	$178.45	$178.50
Purchase #3	$49.81	9.171%	$54.3781	$54.38	$54.40	$54.40
Purchase #4	$238.39	12.215%	$267.5093	$267.51	$267.50	$267.50
Purchase #5	$66.41	13.478%	$75.3607	$75.36	$75.35	$75.40
Purchase #6	$31.40	6.194%	$33.3449	$33.34	$33.35	$33.30
Purchase #7	$91.81	3.388%	$94.9205	$94.92	$94.90	$94.90
7 purchase totals =	$779.65		$855.5271	$855.53	$855.50	$855.50