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	$29.87	4.376%	$31.1771	$31.18	$31.20	$31.20
Purchase #2	$35.54	8.642%	$38.6114	$38.61	$38.60	$38.60
Purchase #3	$55.68	7.195%	$59.6862	$59.69	$59.70	$59.70
Purchase #4	$181.48	3.598%	$188.0097	$188.01	$188.00	$188.00
Purchase #5	$124.70	13.762%	$141.8612	$141.86	$141.85	$141.90
Purchase #6	$134.59	6.516%	$143.3599	$143.36	$143.35	$143.40
Purchase #7	$30.34	13.130%	$34.3236	$34.32	$34.30	$34.30
7 purchase totals =	$592.20		$637.0291	$637.03	$637.00	$637.10