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	$24.73	9.250%	$27.0175	$27.02	$27.00	$27.00
Purchase #2	$49.42	6.753%	$52.7573	$52.76	$52.75	$52.80
Purchase #3	$204.65	5.282%	$215.4596	$215.46	$215.45	$215.50
Purchase #4	$186.93	5.340%	$196.9121	$196.91	$196.90	$196.90
Purchase #5	$239.40	10.137%	$263.668	$263.67	$263.65	$263.70
Purchase #6	$172.88	13.137%	$195.5912	$195.59	$195.60	$195.60
Purchase #7	$106.40	10.246%	$117.3017	$117.30	$117.30	$117.30
7 purchase totals =	$984.41		$1,068.7074	$1,068.71	$1,068.65	$1,068.80