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	$141.60	9.578%	$155.1624	$155.16	$155.15	$155.20
Purchase #2	$39.62	10.284%	$43.6945	$43.69	$43.70	$43.70
Purchase #3	$229.44	11.545%	$255.9288	$255.93	$255.95	$255.90
Purchase #4	$30.88	13.371%	$35.009	$35.01	$35.00	$35.00
Purchase #5	$245.74	6.133%	$260.8112	$260.81	$260.80	$260.80
Purchase #6	$154.32	9.165%	$168.4634	$168.46	$168.45	$168.50
Purchase #7	$69.78	3.335%	$72.1072	$72.11	$72.10	$72.10
7 purchase totals =	$911.38		$991.1765	$991.17	$991.15	$991.20