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	$89.75	9.666%	$98.4252	$98.43	$98.45	$98.40
Purchase #2	$59.42	6.308%	$63.1682	$63.17	$63.15	$63.20
Purchase #3	$222.51	12.416%	$250.1368	$250.14	$250.15	$250.10
Purchase #4	$58.80	11.282%	$65.4338	$65.43	$65.45	$65.40
Purchase #5	$107.57	3.797%	$111.6544	$111.65	$111.65	$111.70
Purchase #6	$15.29	3.529%	$15.8296	$15.83	$15.85	$15.80
Purchase #7	$138.94	12.366%	$156.1213	$156.12	$156.10	$156.10
7 purchase totals =	$692.28		$760.7693	$760.77	$760.80	$760.70