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	$62.52	9.126%	$68.2256	$68.23	$68.25	$68.20
Purchase #2	$82.56	8.281%	$89.3968	$89.40	$89.40	$89.40
Purchase #3	$96.43	9.154%	$105.2572	$105.26	$105.25	$105.30
Purchase #4	$58.73	13.524%	$66.6726	$66.67	$66.65	$66.70
Purchase #5	$185.84	10.321%	$205.0205	$205.02	$205.00	$205.00
Purchase #6	$209.65	10.365%	$231.3802	$231.38	$231.40	$231.40
Purchase #7	$85.44	8.686%	$92.8613	$92.86	$92.85	$92.90
7 purchase totals =	$781.17		$858.8142	$858.82	$858.80	$858.90