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	$38.54	12.776%	$43.4639	$43.46	$43.45	$43.50
Purchase #2	$194.49	10.562%	$215.032	$215.03	$215.05	$215.00
Purchase #3	$160.52	12.604%	$180.7519	$180.75	$180.75	$180.80
Purchase #4	$142.54	8.448%	$154.5818	$154.58	$154.60	$154.60
Purchase #5	$241.60	4.159%	$251.6481	$251.65	$251.65	$251.60
Purchase #6	$37.91	9.399%	$41.4732	$41.47	$41.45	$41.50
Purchase #7	$136.99	10.586%	$151.4918	$151.49	$151.50	$151.50
7 purchase totals =	$952.59		$1,038.4427	$1,038.43	$1,038.45	$1,038.50