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	$74.43	12.411%	$83.6675	$83.67	$83.65	$83.70
Purchase #2	$124.95	13.657%	$142.0144	$142.01	$142.00	$142.00
Purchase #3	$218.25	11.873%	$244.1628	$244.16	$244.15	$244.20
Purchase #4	$78.83	10.228%	$86.8927	$86.89	$86.90	$86.90
Purchase #5	$126.89	13.752%	$144.3399	$144.34	$144.35	$144.30
Purchase #6	$247.91	12.783%	$279.6003	$279.60	$279.60	$279.60
Purchase #7	$14.78	10.482%	$16.3292	$16.33	$16.35	$16.30
7 purchase totals =	$886.04		$997.0068	$997.00	$997.00	$997.00