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	$132.59	8.660%	$144.0723	$144.07	$144.05	$144.10
Purchase #2	$139.56	11.470%	$155.5675	$155.57	$155.55	$155.60
Purchase #3	$16.37	3.112%	$16.8794	$16.88	$16.90	$16.90
Purchase #4	$162.49	6.225%	$172.605	$172.61	$172.60	$172.60
Purchase #5	$37.37	7.578%	$40.2019	$40.20	$40.20	$40.20
Purchase #6	$217.49	10.789%	$240.955	$240.96	$240.95	$241.00
Purchase #7	$82.78	6.386%	$88.0663	$88.07	$88.05	$88.10
7 purchase totals =	$788.65		$858.3474	$858.36	$858.30	$858.50