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	$48.92	7.856%	$52.7632	$52.76	$52.75	$52.80
Purchase #2	$88.64	4.342%	$92.4887	$92.49	$92.50	$92.50
Purchase #3	$35.94	11.348%	$40.0185	$40.02	$40.00	$40.00
Purchase #4	$161.94	3.727%	$167.9755	$167.98	$168.00	$168.00
Purchase #5	$111.46	4.530%	$116.5091	$116.51	$116.50	$116.50
Purchase #6	$140.82	8.148%	$152.294	$152.29	$152.30	$152.30
Purchase #7	$209.82	6.371%	$223.1876	$223.19	$223.20	$223.20
7 purchase totals =	$797.54		$845.2366	$845.24	$845.25	$845.30