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	$130.94	6.830%	$139.8832	$139.88	$139.90	$139.90
Purchase #2	$64.41	6.606%	$68.6649	$68.66	$68.65	$68.70
Purchase #3	$200.83	4.150%	$209.1644	$209.16	$209.15	$209.20
Purchase #4	$239.86	7.820%	$258.6171	$258.62	$258.60	$258.60
Purchase #5	$127.25	4.535%	$133.0208	$133.02	$133.00	$133.00
Purchase #6	$162.45	11.165%	$180.5875	$180.59	$180.60	$180.60
Purchase #7	$83.79	6.599%	$89.3193	$89.32	$89.30	$89.30
7 purchase totals =	$1,009.53		$1,079.2572	$1,079.25	$1,079.20	$1,079.30