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	$101.31	10.340%	$111.7855	$111.79	$111.80	$111.80
Purchase #2	$130.40	5.384%	$137.4207	$137.42	$137.40	$137.40
Purchase #3	$82.61	5.476%	$87.1337	$87.13	$87.15	$87.10
Purchase #4	$103.89	11.157%	$115.481	$115.48	$115.50	$115.50
Purchase #5	$67.75	6.841%	$72.3848	$72.38	$72.40	$72.40
Purchase #6	$52.94	6.573%	$56.4197	$56.42	$56.40	$56.40
Purchase #7	$58.25	12.614%	$65.5977	$65.60	$65.60	$65.60
7 purchase totals =	$597.15		$646.2231	$646.22	$646.25	$646.20