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	$138.97	3.191%	$143.4045	$143.40	$143.40	$143.40
Purchase #2	$41.41	9.619%	$45.3932	$45.39	$45.40	$45.40
Purchase #3	$82.66	8.570%	$89.744	$89.74	$89.75	$89.70
Purchase #4	$204.74	8.311%	$221.7559	$221.76	$221.75	$221.80
Purchase #5	$111.41	6.390%	$118.5291	$118.53	$118.55	$118.50
Purchase #6	$104.27	9.407%	$114.0787	$114.08	$114.10	$114.10
Purchase #7	$20.37	8.678%	$22.1377	$22.14	$22.15	$22.10
7 purchase totals =	$703.83		$755.0431	$755.04	$755.10	$755.00