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	$22.74	3.649%	$23.5698	$23.57	$23.55	$23.60
Purchase #2	$77.93	13.129%	$88.1614	$88.16	$88.15	$88.20
Purchase #3	$226.73	9.651%	$248.6117	$248.61	$248.60	$248.60
Purchase #4	$188.56	4.152%	$196.389	$196.39	$196.40	$196.40
Purchase #5	$74.80	7.607%	$80.49	$80.49	$80.50	$80.50
Purchase #6	$90.43	5.534%	$95.4344	$95.43	$95.45	$95.40
Purchase #7	$203.92	9.489%	$223.27	$223.27	$223.25	$223.30
7 purchase totals =	$885.11		$955.9263	$955.92	$955.90	$956.00