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	$243.61	5.534%	$257.0914	$257.09	$257.10	$257.10
Purchase #2	$192.89	10.857%	$213.8321	$213.83	$213.85	$213.80
Purchase #3	$80.38	13.447%	$91.1887	$91.19	$91.20	$91.20
Purchase #4	$102.46	3.401%	$105.9447	$105.94	$105.95	$105.90
Purchase #5	$198.69	12.581%	$223.6872	$223.69	$223.70	$223.70
Purchase #6	$207.63	12.360%	$233.2931	$233.29	$233.30	$233.30
Purchase #7	$34.99	6.716%	$37.3399	$37.34	$37.35	$37.30
7 purchase totals =	$1,060.65		$1,162.3771	$1,162.37	$1,162.45	$1,162.30