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	$113.47	9.612%	$124.3767	$124.38	$124.40	$124.40
Purchase #2	$131.90	6.873%	$140.9655	$140.97	$140.95	$141.00
Purchase #3	$211.94	4.163%	$220.7631	$220.76	$220.75	$220.80
Purchase #4	$92.38	13.644%	$104.9843	$104.98	$105.00	$105.00
Purchase #5	$19.91	6.375%	$21.1793	$21.18	$21.20	$21.20
Purchase #6	$214.71	5.205%	$225.8857	$225.89	$225.90	$225.90
Purchase #7	$92.94	8.249%	$100.6066	$100.61	$100.60	$100.60
7 purchase totals =	$877.25		$938.7612	$938.77	$938.80	$938.90