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	$167.60	12.226%	$188.0908	$188.09	$188.10	$188.10
Purchase #2	$133.93	4.445%	$139.8832	$139.88	$139.90	$139.90
Purchase #3	$239.49	6.813%	$255.8065	$255.81	$255.80	$255.80
Purchase #4	$187.76	13.540%	$213.1827	$213.18	$213.20	$213.20
Purchase #5	$179.61	5.151%	$188.8617	$188.86	$188.85	$188.90
Purchase #6	$41.83	8.405%	$45.3458	$45.35	$45.35	$45.30
Purchase #7	$224.94	13.415%	$255.1157	$255.12	$255.10	$255.10
7 purchase totals =	$1,175.16		$1,286.2864	$1,286.29	$1,286.30	$1,286.30