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	$89.89	11.150%	$99.9127	$99.91	$99.90	$99.90
Purchase #2	$191.87	11.716%	$214.3495	$214.35	$214.35	$214.30
Purchase #3	$55.69	5.872%	$58.9601	$58.96	$58.95	$59.00
Purchase #4	$66.43	9.420%	$72.6877	$72.69	$72.70	$72.70
Purchase #5	$172.68	3.352%	$178.4682	$178.47	$178.45	$178.50
Purchase #6	$88.25	8.709%	$95.9357	$95.94	$95.95	$95.90
Purchase #7	$37.91	7.628%	$40.8018	$40.80	$40.80	$40.80
7 purchase totals =	$702.72		$761.1157	$761.12	$761.10	$761.10