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	$88.88	10.584%	$98.2871	$98.29	$98.30	$98.30
Purchase #2	$124.98	3.116%	$128.8744	$128.87	$128.85	$128.90
Purchase #3	$89.29	4.635%	$93.4286	$93.43	$93.45	$93.40
Purchase #4	$135.97	5.466%	$143.4021	$143.40	$143.40	$143.40
Purchase #5	$99.75	6.126%	$105.8607	$105.86	$105.85	$105.90
Purchase #6	$53.35	10.466%	$58.9336	$58.93	$58.95	$58.90
Purchase #7	$154.37	9.419%	$168.9101	$168.91	$168.90	$168.90
7 purchase totals =	$746.59		$797.6966	$797.69	$797.70	$797.70