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	$104.92	12.737%	$118.2837	$118.28	$118.30	$118.30
Purchase #2	$229.56	8.158%	$248.2875	$248.29	$248.30	$248.30
Purchase #3	$246.65	13.219%	$279.2547	$279.25	$279.25	$279.30
Purchase #4	$81.93	12.380%	$92.0729	$92.07	$92.05	$92.10
Purchase #5	$133.79	6.593%	$142.6108	$142.61	$142.60	$142.60
Purchase #6	$48.56	6.440%	$51.6873	$51.69	$51.70	$51.70
Purchase #7	$130.74	13.804%	$148.7873	$148.79	$148.80	$148.80
7 purchase totals =	$976.15		$1,080.9842	$1,080.98	$1,081.00	$1,081.10