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	$77.40	5.197%	$81.4225	$81.42	$81.40	$81.40
Purchase #2	$193.44	11.457%	$215.6024	$215.60	$215.60	$215.60
Purchase #3	$97.79	9.761%	$107.3353	$107.34	$107.35	$107.30
Purchase #4	$222.25	5.694%	$234.9049	$234.90	$234.90	$234.90
Purchase #5	$226.29	12.626%	$254.8614	$254.86	$254.85	$254.90
Purchase #6	$242.83	7.799%	$261.7683	$261.77	$261.75	$261.80
Purchase #7	$40.45	11.202%	$44.9812	$44.98	$45.00	$45.00
7 purchase totals =	$1,100.45		$1,200.8760	$1,200.87	$1,200.85	$1,200.90