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	$137.69	11.144%	$153.0342	$153.03	$153.05	$153.00
Purchase #2	$90.54	4.834%	$94.9167	$94.92	$94.90	$94.90
Purchase #3	$197.81	10.470%	$218.5207	$218.52	$218.50	$218.50
Purchase #4	$146.82	13.441%	$166.5541	$166.55	$166.55	$166.60
Purchase #5	$90.96	13.105%	$102.8803	$102.88	$102.90	$102.90
Purchase #6	$91.94	12.138%	$103.0997	$103.10	$103.10	$103.10
Purchase #7	$36.43	12.346%	$40.9276	$40.93	$40.95	$40.90
7 purchase totals =	$792.19		$879.9333	$879.93	$879.95	$879.90