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	$50.94	6.725%	$54.3657	$54.37	$54.35	$54.40
Purchase #2	$107.89	12.749%	$121.6449	$121.64	$121.65	$121.60
Purchase #3	$211.42	7.801%	$227.9129	$227.91	$227.90	$227.90
Purchase #4	$113.32	12.360%	$127.3264	$127.33	$127.35	$127.30
Purchase #5	$109.32	6.360%	$116.2728	$116.27	$116.25	$116.30
Purchase #6	$73.90	3.490%	$76.4791	$76.48	$76.50	$76.50
Purchase #7	$111.50	4.851%	$116.9089	$116.91	$116.90	$116.90
7 purchase totals =	$778.29		$840.9107	$840.91	$840.90	$840.90