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	$72.48	8.127%	$78.3704	$78.37	$78.35	$78.40
Purchase #2	$55.97	10.353%	$61.7646	$61.76	$61.75	$61.80
Purchase #3	$144.40	8.742%	$157.0234	$157.02	$157.00	$157.00
Purchase #4	$19.31	6.527%	$20.5704	$20.57	$20.55	$20.60
Purchase #5	$132.42	6.319%	$140.7876	$140.79	$140.80	$140.80
Purchase #6	$58.64	8.850%	$63.8296	$63.83	$63.85	$63.80
Purchase #7	$9.26	13.211%	$10.4833	$10.48	$10.50	$10.50
7 purchase totals =	$492.48		$532.8293	$532.82	$532.80	$532.90