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	$37.64	4.426%	$39.3059	$39.31	$39.30	$39.30
Purchase #2	$156.98	12.260%	$176.2257	$176.23	$176.25	$176.20
Purchase #3	$32.96	7.572%	$35.4557	$35.46	$35.45	$35.50
Purchase #4	$114.82	3.753%	$119.1292	$119.13	$119.15	$119.10
Purchase #5	$137.60	10.804%	$152.4663	$152.47	$152.45	$152.50
Purchase #6	$6.88	4.683%	$7.2022	$7.20	$7.20	$7.20
Purchase #7	$72.46	7.489%	$77.8865	$77.89	$77.90	$77.90
7 purchase totals =	$559.34		$607.6715	$607.69	$607.70	$607.70