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	$94.31	10.309%	$104.0324	$104.03	$104.05	$104.00
Purchase #2	$89.54	13.684%	$101.7927	$101.79	$101.80	$101.80
Purchase #3	$73.60	4.123%	$76.6345	$76.63	$76.65	$76.60
Purchase #4	$42.77	8.860%	$46.5594	$46.56	$46.55	$46.60
Purchase #5	$19.41	7.278%	$20.8227	$20.82	$20.80	$20.80
Purchase #6	$24.90	10.573%	$27.5327	$27.53	$27.55	$27.50
Purchase #7	$12.99	3.715%	$13.4726	$13.47	$13.45	$13.50
7 purchase totals =	$357.52		$390.8470	$390.83	$390.85	$390.80