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	$205.38	13.656%	$233.4267	$233.43	$233.45	$233.40
Purchase #2	$150.55	13.437%	$170.7794	$170.78	$170.80	$170.80
Purchase #3	$56.44	5.628%	$59.6164	$59.62	$59.60	$59.60
Purchase #4	$127.31	6.804%	$135.9722	$135.97	$135.95	$136.00
Purchase #5	$69.38	6.393%	$73.8155	$73.82	$73.80	$73.80
Purchase #6	$128.97	10.240%	$142.1765	$142.18	$142.20	$142.20
Purchase #7	$29.45	10.148%	$32.4386	$32.44	$32.45	$32.40
7 purchase totals =	$767.48		$848.2253	$848.24	$848.25	$848.20