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	$96.35	3.580%	$99.7993	$99.80	$99.80	$99.80
Purchase #2	$82.93	11.480%	$92.4504	$92.45	$92.45	$92.50
Purchase #3	$10.45	13.508%	$11.8616	$11.86	$11.85	$11.90
Purchase #4	$39.72	13.809%	$45.2049	$45.20	$45.20	$45.20
Purchase #5	$8.37	4.691%	$8.7626	$8.76	$8.75	$8.80
Purchase #6	$250.76	11.845%	$280.4625	$280.46	$280.45	$280.50
Purchase #7	$7.54	4.614%	$7.8879	$7.89	$7.90	$7.90
7 purchase totals =	$496.12		$546.4292	$546.42	$546.40	$546.60