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	$123.91	11.593%	$138.2749	$138.27	$138.25	$138.30
Purchase #2	$236.26	10.262%	$260.505	$260.51	$260.50	$260.50
Purchase #3	$146.52	12.300%	$164.542	$164.54	$164.55	$164.50
Purchase #4	$136.32	10.578%	$150.7399	$150.74	$150.75	$150.70
Purchase #5	$249.77	10.668%	$276.4155	$276.42	$276.40	$276.40
Purchase #6	$156.79	5.860%	$165.9779	$165.98	$166.00	$166.00
Purchase #7	$142.53	6.102%	$151.2272	$151.23	$151.25	$151.20
7 purchase totals =	$1,192.10		$1,307.6824	$1,307.69	$1,307.70	$1,307.60