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	$103.96	4.146%	$108.2702	$108.27	$108.25	$108.30
Purchase #2	$190.86	12.668%	$215.0381	$215.04	$215.05	$215.00
Purchase #3	$195.80	9.307%	$214.0231	$214.02	$214.00	$214.00
Purchase #4	$40.59	3.217%	$41.8958	$41.90	$41.90	$41.90
Purchase #5	$50.52	10.565%	$55.8574	$55.86	$55.85	$55.90
Purchase #6	$83.69	10.343%	$92.3461	$92.35	$92.35	$92.30
Purchase #7	$50.26	5.733%	$53.1414	$53.14	$53.15	$53.10
7 purchase totals =	$715.68		$780.5721	$780.58	$780.55	$780.50