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	$160.55	11.651%	$179.2557	$179.26	$179.25	$179.30
Purchase #2	$190.48	13.871%	$216.9015	$216.90	$216.90	$216.90
Purchase #3	$211.46	12.828%	$238.5861	$238.59	$238.60	$238.60
Purchase #4	$239.46	10.192%	$263.8658	$263.87	$263.85	$263.90
Purchase #5	$49.85	11.485%	$55.5753	$55.58	$55.60	$55.60
Purchase #6	$116.39	8.435%	$126.2075	$126.21	$126.20	$126.20
Purchase #7	$86.31	3.173%	$89.0486	$89.05	$89.05	$89.00
7 purchase totals =	$1,054.50		$1,169.4405	$1,169.46	$1,169.45	$1,169.50