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	$22.33	3.250%	$23.0557	$23.06	$23.05	$23.10
Purchase #2	$176.69	6.109%	$187.484	$187.48	$187.50	$187.50
Purchase #3	$147.64	12.648%	$166.3135	$166.31	$166.30	$166.30
Purchase #4	$81.60	12.792%	$92.0383	$92.04	$92.05	$92.00
Purchase #5	$37.56	8.659%	$40.8123	$40.81	$40.80	$40.80
Purchase #6	$55.65	7.498%	$59.8226	$59.82	$59.80	$59.80
Purchase #7	$46.76	7.356%	$50.1997	$50.20	$50.20	$50.20
7 purchase totals =	$568.23		$619.7261	$619.72	$619.70	$619.70