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	$110.48	11.537%	$123.2261	$123.23	$123.25	$123.20
Purchase #2	$169.50	12.474%	$190.6434	$190.64	$190.65	$190.60
Purchase #3	$85.50	13.239%	$96.8193	$96.82	$96.80	$96.80
Purchase #4	$71.30	4.799%	$74.7217	$74.72	$74.70	$74.70
Purchase #5	$60.87	13.160%	$68.8805	$68.88	$68.90	$68.90
Purchase #6	$171.47	4.656%	$179.4536	$179.45	$179.45	$179.50
Purchase #7	$18.78	11.344%	$20.9104	$20.91	$20.90	$20.90
7 purchase totals =	$687.90		$754.6550	$754.65	$754.65	$754.60