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	$93.64	11.604%	$104.506	$104.51	$104.50	$104.50
Purchase #2	$153.66	8.238%	$166.3185	$166.32	$166.30	$166.30
Purchase #3	$64.81	11.728%	$72.4109	$72.41	$72.40	$72.40
Purchase #4	$215.42	7.269%	$231.0789	$231.08	$231.10	$231.10
Purchase #5	$27.52	5.538%	$29.0441	$29.04	$29.05	$29.00
Purchase #6	$130.72	13.589%	$148.4835	$148.48	$148.50	$148.50
Purchase #7	$62.32	12.614%	$70.181	$70.18	$70.20	$70.20
7 purchase totals =	$748.09		$822.0229	$822.02	$822.05	$822.00