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	$88.96	13.392%	$100.8735	$100.87	$100.85	$100.90
Purchase #2	$190.30	3.228%	$196.4429	$196.44	$196.45	$196.40
Purchase #3	$187.91	7.221%	$201.479	$201.48	$201.50	$201.50
Purchase #4	$205.75	8.227%	$222.6771	$222.68	$222.70	$222.70
Purchase #5	$124.28	9.662%	$136.2879	$136.29	$136.30	$136.30
Purchase #6	$26.73	7.116%	$28.6321	$28.63	$28.65	$28.60
Purchase #7	$31.48	4.548%	$32.9117	$32.91	$32.90	$32.90
7 purchase totals =	$855.41		$919.3042	$919.30	$919.35	$919.30