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	$66.97	8.859%	$72.9029	$72.90	$72.90	$72.90
Purchase #2	$116.53	10.257%	$128.4825	$128.48	$128.50	$128.50
Purchase #3	$36.93	9.396%	$40.3999	$40.40	$40.40	$40.40
Purchase #4	$202.92	9.282%	$221.755	$221.76	$221.75	$221.80
Purchase #5	$33.33	4.578%	$34.8558	$34.86	$34.85	$34.90
Purchase #6	$148.77	4.471%	$155.4215	$155.42	$155.40	$155.40
Purchase #7	$6.58	10.691%	$7.2835	$7.28	$7.30	$7.30
7 purchase totals =	$612.03		$661.1011	$661.10	$661.10	$661.20