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	$86.34	4.104%	$89.8834	$89.88	$89.90	$89.90
Purchase #2	$208.53	3.374%	$215.5658	$215.57	$215.55	$215.60
Purchase #3	$139.40	10.750%	$154.3855	$154.39	$154.40	$154.40
Purchase #4	$172.47	8.650%	$187.3887	$187.39	$187.40	$187.40
Purchase #5	$65.29	8.475%	$70.8233	$70.82	$70.80	$70.80
Purchase #6	$85.85	3.163%	$88.5654	$88.57	$88.55	$88.60
Purchase #7	$97.82	11.612%	$109.1789	$109.18	$109.20	$109.20
7 purchase totals =	$855.70		$915.7910	$915.80	$915.80	$915.90