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	$168.72	6.561%	$179.7897	$179.79	$179.80	$179.80
Purchase #2	$106.30	5.159%	$111.784	$111.78	$111.80	$111.80
Purchase #3	$151.91	13.602%	$172.5728	$172.57	$172.55	$172.60
Purchase #4	$208.70	4.840%	$218.8011	$218.80	$218.80	$218.80
Purchase #5	$11.42	13.283%	$12.9369	$12.94	$12.95	$12.90
Purchase #6	$29.70	7.369%	$31.8886	$31.89	$31.90	$31.90
Purchase #7	$21.80	7.599%	$23.4566	$23.46	$23.45	$23.50
7 purchase totals =	$698.55		$751.2297	$751.23	$751.25	$751.30