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	$115.83	12.603%	$130.4281	$130.43	$130.45	$130.40
Purchase #2	$127.50	5.596%	$134.6349	$134.63	$134.65	$134.60
Purchase #3	$250.73	13.734%	$285.1653	$285.17	$285.15	$285.20
Purchase #4	$83.99	8.204%	$90.8805	$90.88	$90.90	$90.90
Purchase #5	$82.93	3.516%	$85.8458	$85.85	$85.85	$85.80
Purchase #6	$6.56	10.462%	$7.2463	$7.25	$7.25	$7.20
Purchase #7	$159.32	7.487%	$171.2483	$171.25	$171.25	$171.20
7 purchase totals =	$826.86		$905.4492	$905.46	$905.50	$905.30