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	$173.25	4.811%	$181.5851	$181.59	$181.60	$181.60
Purchase #2	$79.86	12.837%	$90.1116	$90.11	$90.10	$90.10
Purchase #3	$203.80	13.634%	$231.5861	$231.59	$231.60	$231.60
Purchase #4	$49.46	12.148%	$55.4684	$55.47	$55.45	$55.50
Purchase #5	$58.81	7.217%	$63.0543	$63.05	$63.05	$63.10
Purchase #6	$82.95	11.642%	$92.607	$92.61	$92.60	$92.60
Purchase #7	$139.64	7.725%	$150.4272	$150.43	$150.45	$150.40
7 purchase totals =	$787.77		$864.8397	$864.85	$864.85	$864.90