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	$99.27	12.219%	$111.3998	$111.40	$111.40	$111.40
Purchase #2	$238.29	3.558%	$246.7684	$246.77	$246.75	$246.80
Purchase #3	$125.68	10.857%	$139.3251	$139.33	$139.35	$139.30
Purchase #4	$127.37	13.318%	$144.3331	$144.33	$144.35	$144.30
Purchase #5	$33.47	4.800%	$35.0766	$35.08	$35.10	$35.10
Purchase #6	$117.74	6.541%	$125.4414	$125.44	$125.45	$125.40
Purchase #7	$89.77	12.437%	$100.9347	$100.93	$100.95	$100.90
7 purchase totals =	$831.59		$903.2791	$903.28	$903.35	$903.20