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	$204.80	11.745%	$228.8538	$228.85	$228.85	$228.90
Purchase #2	$133.53	8.268%	$144.5703	$144.57	$144.55	$144.60
Purchase #3	$179.62	8.508%	$194.9021	$194.90	$194.90	$194.90
Purchase #4	$20.72	3.463%	$21.4375	$21.44	$21.45	$21.40
Purchase #5	$64.52	5.213%	$67.8834	$67.88	$67.90	$67.90
Purchase #6	$88.51	4.673%	$92.6461	$92.65	$92.65	$92.60
Purchase #7	$171.91	9.345%	$187.975	$187.98	$188.00	$188.00
7 purchase totals =	$863.61		$938.2682	$938.27	$938.30	$938.30