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	$83.29	8.660%	$90.5029	$90.50	$90.50	$90.50
Purchase #2	$44.32	10.860%	$49.1332	$49.13	$49.15	$49.10
Purchase #3	$196.36	11.833%	$219.5953	$219.60	$219.60	$219.60
Purchase #4	$164.40	12.498%	$184.9467	$184.95	$184.95	$184.90
Purchase #5	$52.62	13.330%	$59.6342	$59.63	$59.65	$59.60
Purchase #6	$131.95	10.449%	$145.7375	$145.74	$145.75	$145.70
Purchase #7	$234.60	6.686%	$250.2854	$250.29	$250.30	$250.30
7 purchase totals =	$907.54		$999.8352	$999.84	$999.90	$999.70