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	$210.45	13.383%	$238.6145	$238.61	$238.60	$238.60
Purchase #2	$51.51	11.704%	$57.5387	$57.54	$57.55	$57.50
Purchase #3	$106.76	10.830%	$118.3221	$118.32	$118.30	$118.30
Purchase #4	$15.69	11.227%	$17.4515	$17.45	$17.45	$17.50
Purchase #5	$92.51	11.278%	$102.9433	$102.94	$102.95	$102.90
Purchase #6	$182.88	9.544%	$200.3341	$200.33	$200.35	$200.30
Purchase #7	$68.27	13.474%	$77.4687	$77.47	$77.45	$77.50
7 purchase totals =	$728.07		$812.6729	$812.66	$812.65	$812.60