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	$58.39	13.714%	$66.3976	$66.40	$66.40	$66.40
Purchase #2	$64.89	11.357%	$72.2596	$72.26	$72.25	$72.30
Purchase #3	$172.72	4.685%	$180.8119	$180.81	$180.80	$180.80
Purchase #4	$126.25	3.694%	$130.9137	$130.91	$130.90	$130.90
Purchase #5	$82.46	12.681%	$92.9168	$92.92	$92.90	$92.90
Purchase #6	$199.80	11.419%	$222.6152	$222.62	$222.60	$222.60
Purchase #7	$50.95	13.759%	$57.9602	$57.96	$57.95	$58.00
7 purchase totals =	$755.46		$823.8750	$823.88	$823.80	$823.90