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	$232.50	9.644%	$254.9223	$254.92	$254.90	$254.90
Purchase #2	$25.65	6.223%	$27.2462	$27.25	$27.25	$27.20
Purchase #3	$45.95	8.637%	$49.9187	$49.92	$49.90	$49.90
Purchase #4	$45.72	10.609%	$50.5704	$50.57	$50.55	$50.60
Purchase #5	$70.56	10.564%	$78.014	$78.01	$78.00	$78.00
Purchase #6	$148.62	8.208%	$160.8187	$160.82	$160.80	$160.80
Purchase #7	$38.60	12.586%	$43.4582	$43.46	$43.45	$43.50
7 purchase totals =	$607.60		$664.9485	$664.95	$664.85	$664.90