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	$64.66	12.762%	$72.9119	$72.91	$72.90	$72.90
Purchase #2	$40.44	10.394%	$44.6433	$44.64	$44.65	$44.60
Purchase #3	$101.72	4.144%	$105.9353	$105.94	$105.95	$105.90
Purchase #4	$109.39	9.581%	$119.8707	$119.87	$119.85	$119.90
Purchase #5	$207.89	5.693%	$219.7252	$219.73	$219.75	$219.70
Purchase #6	$52.46	10.400%	$57.9158	$57.92	$57.90	$57.90
Purchase #7	$30.62	9.521%	$33.5353	$33.54	$33.55	$33.50
7 purchase totals =	$607.18		$654.5375	$654.55	$654.55	$654.40