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	$87.95	7.386%	$94.446	$94.45	$94.45	$94.40
Purchase #2	$99.89	9.222%	$109.1019	$109.10	$109.10	$109.10
Purchase #3	$44.67	11.375%	$49.7512	$49.75	$49.75	$49.80
Purchase #4	$80.72	12.782%	$91.0376	$91.04	$91.05	$91.00
Purchase #5	$59.82	6.303%	$63.5905	$63.59	$63.60	$63.60
Purchase #6	$76.55	8.560%	$83.1027	$83.10	$83.10	$83.10
Purchase #7	$85.43	4.354%	$89.1496	$89.15	$89.15	$89.10
7 purchase totals =	$535.03		$580.1795	$580.18	$580.20	$580.10