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	$111.84	5.847%	$118.3793	$118.38	$118.40	$118.40
Purchase #2	$114.34	11.782%	$127.8115	$127.81	$127.80	$127.80
Purchase #3	$146.32	10.771%	$162.0801	$162.08	$162.10	$162.10
Purchase #4	$24.90	4.562%	$26.0359	$26.04	$26.05	$26.00
Purchase #5	$102.56	9.445%	$112.2468	$112.25	$112.25	$112.20
Purchase #6	$93.36	10.732%	$103.3794	$103.38	$103.40	$103.40
Purchase #7	$178.97	9.723%	$196.3713	$196.37	$196.35	$196.40
7 purchase totals =	$772.29		$846.3043	$846.31	$846.35	$846.30