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	$80.82	12.642%	$91.0373	$91.04	$91.05	$91.00
Purchase #2	$59.59	9.250%	$65.1021	$65.10	$65.10	$65.10
Purchase #3	$64.80	5.452%	$68.3329	$68.33	$68.35	$68.30
Purchase #4	$124.53	9.761%	$136.6854	$136.69	$136.70	$136.70
Purchase #5	$141.89	6.327%	$150.8674	$150.87	$150.85	$150.90
Purchase #6	$58.73	10.766%	$65.0529	$65.05	$65.05	$65.10
Purchase #7	$95.79	7.590%	$103.0605	$103.06	$103.05	$103.10
7 purchase totals =	$626.15		$680.1385	$680.14	$680.15	$680.20