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	$78.62	13.842%	$89.5026	$89.50	$89.50	$89.50
Purchase #2	$108.82	11.460%	$121.2908	$121.29	$121.30	$121.30
Purchase #3	$120.29	3.123%	$124.0467	$124.05	$124.05	$124.00
Purchase #4	$203.80	13.398%	$231.1051	$231.11	$231.10	$231.10
Purchase #5	$80.30	9.733%	$88.1156	$88.12	$88.10	$88.10
Purchase #6	$133.57	10.497%	$147.5908	$147.59	$147.60	$147.60
Purchase #7	$180.83	6.692%	$192.9311	$192.93	$192.95	$192.90
7 purchase totals =	$906.23		$994.5827	$994.59	$994.60	$994.50