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	$130.60	6.669%	$139.3097	$139.31	$139.30	$139.30
Purchase #2	$137.80	12.436%	$154.9368	$154.94	$154.95	$154.90
Purchase #3	$15.99	6.365%	$17.0078	$17.01	$17.00	$17.00
Purchase #4	$50.90	7.149%	$54.5388	$54.54	$54.55	$54.50
Purchase #5	$65.77	10.830%	$72.8929	$72.89	$72.90	$72.90
Purchase #6	$137.98	4.258%	$143.8552	$143.86	$143.85	$143.90
Purchase #7	$149.51	6.419%	$159.107	$159.11	$159.10	$159.10
7 purchase totals =	$688.55		$741.6482	$741.66	$741.65	$741.60