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	$49.51	9.312%	$54.1204	$54.12	$54.10	$54.10
Purchase #2	$83.87	3.609%	$86.8969	$86.90	$86.90	$86.90
Purchase #3	$35.97	7.627%	$38.7134	$38.71	$38.70	$38.70
Purchase #4	$73.68	6.197%	$78.2459	$78.25	$78.25	$78.20
Purchase #5	$37.72	3.823%	$39.162	$39.16	$39.15	$39.20
Purchase #6	$126.61	11.498%	$141.1676	$141.17	$141.15	$141.20
Purchase #7	$97.62	4.648%	$102.1574	$102.16	$102.15	$102.20
7 purchase totals =	$504.98		$540.4636	$540.47	$540.40	$540.50