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	$43.31	4.275%	$45.1615	$45.16	$45.15	$45.20
Purchase #2	$122.38	12.397%	$137.5514	$137.55	$137.55	$137.60
Purchase #3	$209.86	3.726%	$217.6794	$217.68	$217.70	$217.70
Purchase #4	$77.95	6.363%	$82.91	$82.91	$82.90	$82.90
Purchase #5	$75.76	10.345%	$83.5974	$83.60	$83.60	$83.60
Purchase #6	$75.25	4.619%	$78.7258	$78.73	$78.75	$78.70
Purchase #7	$187.96	13.748%	$213.8007	$213.80	$213.80	$213.80
7 purchase totals =	$792.47		$859.4262	$859.43	$859.45	$859.50