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	$148.92	4.472%	$155.5797	$155.58	$155.60	$155.60
Purchase #2	$60.26	10.273%	$66.4505	$66.45	$66.45	$66.50
Purchase #3	$40.86	4.695%	$42.7784	$42.78	$42.80	$42.80
Purchase #4	$82.82	7.281%	$88.8501	$88.85	$88.85	$88.90
Purchase #5	$10.33	10.513%	$11.416	$11.42	$11.40	$11.40
Purchase #6	$21.99	12.857%	$24.8173	$24.82	$24.80	$24.80
Purchase #7	$80.58	12.837%	$90.9241	$90.92	$90.90	$90.90
7 purchase totals =	$445.76		$480.8161	$480.82	$480.80	$480.90