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	$88.73	13.390%	$100.6109	$100.61	$100.60	$100.60
Purchase #2	$102.33	12.166%	$114.7795	$114.78	$114.80	$114.80
Purchase #3	$225.29	13.544%	$255.8033	$255.80	$255.80	$255.80
Purchase #4	$167.74	9.682%	$183.9806	$183.98	$184.00	$184.00
Purchase #5	$136.37	7.474%	$146.5623	$146.56	$146.55	$146.60
Purchase #6	$237.34	10.103%	$261.3185	$261.32	$261.30	$261.30
Purchase #7	$111.82	3.375%	$115.5939	$115.59	$115.60	$115.60
7 purchase totals =	$1,069.62		$1,178.6490	$1,178.64	$1,178.65	$1,178.70