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	$147.81	12.827%	$166.7696	$166.77	$166.75	$166.80
Purchase #2	$123.92	13.686%	$140.8797	$140.88	$140.90	$140.90
Purchase #3	$84.59	12.136%	$94.8558	$94.86	$94.85	$94.90
Purchase #4	$49.28	5.794%	$52.1353	$52.14	$52.15	$52.10
Purchase #5	$87.28	13.697%	$99.2347	$99.23	$99.25	$99.20
Purchase #6	$178.86	9.873%	$196.5188	$196.52	$196.50	$196.50
Purchase #7	$111.65	12.439%	$125.5381	$125.54	$125.55	$125.50
7 purchase totals =	$783.39		$875.9320	$875.94	$875.95	$875.90