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	$108.33	3.610%	$112.2407	$112.24	$112.25	$112.20
Purchase #2	$135.44	8.211%	$146.561	$146.56	$146.55	$146.60
Purchase #3	$205.28	4.164%	$213.8279	$213.83	$213.85	$213.80
Purchase #4	$52.40	10.525%	$57.9151	$57.92	$57.90	$57.90
Purchase #5	$6.35	13.772%	$7.2245	$7.22	$7.20	$7.20
Purchase #6	$127.71	11.373%	$142.2345	$142.23	$142.25	$142.20
Purchase #7	$141.89	6.708%	$151.408	$151.41	$151.40	$151.40
7 purchase totals =	$777.40		$831.4117	$831.41	$831.40	$831.30