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	$128.74	12.229%	$144.4836	$144.48	$144.50	$144.50
Purchase #2	$129.77	11.190%	$144.2913	$144.29	$144.30	$144.30
Purchase #3	$170.69	12.664%	$192.3062	$192.31	$192.30	$192.30
Purchase #4	$77.77	9.681%	$85.2989	$85.30	$85.30	$85.30
Purchase #5	$73.74	11.378%	$82.1301	$82.13	$82.15	$82.10
Purchase #6	$242.45	9.715%	$266.004	$266.00	$266.00	$266.00
Purchase #7	$97.31	8.725%	$105.8003	$105.80	$105.80	$105.80
7 purchase totals =	$920.47		$1,020.3144	$1,020.31	$1,020.35	$1,020.30