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	$55.65	13.191%	$62.9908	$62.99	$63.00	$63.00
Purchase #2	$28.77	3.160%	$29.6791	$29.68	$29.70	$29.70
Purchase #3	$78.67	6.410%	$83.7127	$83.71	$83.70	$83.70
Purchase #4	$232.88	3.500%	$241.0308	$241.03	$241.05	$241.00
Purchase #5	$34.39	8.313%	$37.2488	$37.25	$37.25	$37.20
Purchase #6	$212.67	13.233%	$240.8126	$240.81	$240.80	$240.80
Purchase #7	$78.52	13.862%	$89.4044	$89.40	$89.40	$89.40
7 purchase totals =	$721.55		$784.8792	$784.87	$784.90	$784.80