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	$39.87	4.563%	$41.6893	$41.69	$41.70	$41.70
Purchase #2	$166.40	6.256%	$176.81	$176.81	$176.80	$176.80
Purchase #3	$32.42	10.451%	$35.8082	$35.81	$35.80	$35.80
Purchase #4	$31.32	6.639%	$33.3993	$33.40	$33.40	$33.40
Purchase #5	$38.47	5.583%	$40.6178	$40.62	$40.60	$40.60
Purchase #6	$29.59	11.215%	$32.9085	$32.91	$32.90	$32.90
Purchase #7	$109.46	7.221%	$117.3641	$117.36	$117.35	$117.40
7 purchase totals =	$447.53		$478.5972	$478.60	$478.55	$478.60