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	$69.90	11.253%	$77.7658	$77.77	$77.75	$77.80
Purchase #2	$34.72	5.147%	$36.507	$36.51	$36.50	$36.50
Purchase #3	$105.38	8.671%	$114.5175	$114.52	$114.50	$114.50
Purchase #4	$244.53	12.595%	$275.3286	$275.33	$275.35	$275.30
Purchase #5	$107.73	5.168%	$113.2975	$113.30	$113.30	$113.30
Purchase #6	$83.85	4.344%	$87.4924	$87.49	$87.50	$87.50
Purchase #7	$92.71	11.552%	$103.4199	$103.42	$103.40	$103.40
7 purchase totals =	$738.82		$808.3287	$808.34	$808.30	$808.30