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	$23.76	5.205%	$24.9967	$25.00	$25.00	$25.00
Purchase #2	$101.27	10.375%	$111.7768	$111.78	$111.80	$111.80
Purchase #3	$75.90	9.109%	$82.8137	$82.81	$82.80	$82.80
Purchase #4	$93.99	5.575%	$99.2299	$99.23	$99.25	$99.20
Purchase #5	$199.39	4.450%	$208.2629	$208.26	$208.25	$208.30
Purchase #6	$155.84	6.785%	$166.4137	$166.41	$166.40	$166.40
Purchase #7	$198.97	12.547%	$223.9348	$223.93	$223.95	$223.90
7 purchase totals =	$849.12		$917.4285	$917.42	$917.45	$917.40