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	$40.37	7.244%	$43.2944	$43.29	$43.30	$43.30
Purchase #2	$67.54	5.311%	$71.127	$71.13	$71.15	$71.10
Purchase #3	$194.82	5.780%	$206.0806	$206.08	$206.10	$206.10
Purchase #4	$109.41	8.486%	$118.6945	$118.69	$118.70	$118.70
Purchase #5	$54.92	3.448%	$56.8136	$56.81	$56.80	$56.80
Purchase #6	$136.87	12.191%	$153.5558	$153.56	$153.55	$153.60
Purchase #7	$141.70	6.239%	$150.5407	$150.54	$150.55	$150.50
7 purchase totals =	$745.63		$800.1066	$800.10	$800.15	$800.10