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	$45.90	10.715%	$50.8182	$50.82	$50.80	$50.80
Purchase #2	$172.64	7.288%	$185.222	$185.22	$185.20	$185.20
Purchase #3	$212.57	4.821%	$222.818	$222.82	$222.80	$222.80
Purchase #4	$119.90	13.219%	$135.7496	$135.75	$135.75	$135.70
Purchase #5	$33.40	12.156%	$37.4601	$37.46	$37.45	$37.50
Purchase #6	$122.83	9.601%	$134.6229	$134.62	$134.60	$134.60
Purchase #7	$75.50	3.429%	$78.0889	$78.09	$78.10	$78.10
7 purchase totals =	$782.74		$844.7797	$844.78	$844.70	$844.70