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	$84.25	6.749%	$89.936	$89.94	$89.95	$89.90
Purchase #2	$202.35	12.116%	$226.8667	$226.87	$226.85	$226.90
Purchase #3	$206.83	7.714%	$222.7849	$222.78	$222.80	$222.80
Purchase #4	$152.77	8.356%	$165.5355	$165.54	$165.55	$165.50
Purchase #5	$204.99	3.281%	$211.7157	$211.72	$211.70	$211.70
Purchase #6	$201.84	3.192%	$208.2827	$208.28	$208.30	$208.30
Purchase #7	$179.26	6.205%	$190.3831	$190.38	$190.40	$190.40
7 purchase totals =	$1,232.29		$1,315.5046	$1,315.51	$1,315.55	$1,315.50