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	$75.82	12.229%	$85.092	$85.09	$85.10	$85.10
Purchase #2	$218.28	12.133%	$244.7639	$244.76	$244.75	$244.80
Purchase #3	$231.83	10.190%	$255.4535	$255.45	$255.45	$255.50
Purchase #4	$146.61	10.548%	$162.0744	$162.07	$162.05	$162.10
Purchase #5	$94.58	9.159%	$103.2426	$103.24	$103.25	$103.20
Purchase #6	$74.69	5.155%	$78.5403	$78.54	$78.55	$78.50
Purchase #7	$9.97	7.809%	$10.7486	$10.75	$10.75	$10.70
7 purchase totals =	$851.78		$939.9153	$939.90	$939.90	$939.90