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	$29.66	12.176%	$33.2714	$33.27	$33.25	$33.30
Purchase #2	$31.45	4.126%	$32.7476	$32.75	$32.75	$32.70
Purchase #3	$178.61	10.231%	$196.8836	$196.88	$196.90	$196.90
Purchase #4	$223.74	9.634%	$245.2951	$245.30	$245.30	$245.30
Purchase #5	$99.95	13.868%	$113.8111	$113.81	$113.80	$113.80
Purchase #6	$100.38	13.772%	$114.2043	$114.20	$114.20	$114.20
Purchase #7	$96.66	8.826%	$105.1912	$105.19	$105.20	$105.20
7 purchase totals =	$760.45		$841.4043	$841.40	$841.40	$841.40