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	$240.59	7.243%	$258.0159	$258.02	$258.00	$258.00
Purchase #2	$212.53	4.681%	$222.4785	$222.48	$222.50	$222.50
Purchase #3	$74.54	6.234%	$79.1868	$79.19	$79.20	$79.20
Purchase #4	$155.92	10.723%	$172.6393	$172.64	$172.65	$172.60
Purchase #5	$94.78	6.503%	$100.9435	$100.94	$100.95	$100.90
Purchase #6	$48.69	4.596%	$50.9278	$50.93	$50.95	$50.90
Purchase #7	$26.85	8.501%	$29.1325	$29.13	$29.15	$29.10
7 purchase totals =	$853.90		$913.3243	$913.33	$913.40	$913.20