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	$61.31	4.736%	$64.2136	$64.21	$64.20	$64.20
Purchase #2	$39.60	7.178%	$42.4425	$42.44	$42.45	$42.40
Purchase #3	$242.78	12.189%	$272.3725	$272.37	$272.35	$272.40
Purchase #4	$48.82	8.126%	$52.7871	$52.79	$52.80	$52.80
Purchase #5	$96.99	7.465%	$104.2303	$104.23	$104.25	$104.20
Purchase #6	$37.67	6.486%	$40.1133	$40.11	$40.10	$40.10
Purchase #7	$80.31	13.342%	$91.025	$91.03	$91.05	$91.00
7 purchase totals =	$607.48		$667.1843	$667.18	$667.20	$667.10