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	$44.70	6.190%	$47.4669	$47.47	$47.45	$47.50
Purchase #2	$37.74	3.507%	$39.0635	$39.06	$39.05	$39.10
Purchase #3	$89.92	13.792%	$102.3218	$102.32	$102.30	$102.30
Purchase #4	$28.68	9.852%	$31.5056	$31.51	$31.50	$31.50
Purchase #5	$50.67	6.456%	$53.9413	$53.94	$53.95	$53.90
Purchase #6	$108.46	4.673%	$113.5283	$113.53	$113.55	$113.50
Purchase #7	$175.79	8.320%	$190.4157	$190.42	$190.40	$190.40
7 purchase totals =	$535.96		$578.2431	$578.25	$578.20	$578.20