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	$136.50	6.866%	$145.8721	$145.87	$145.85	$145.90
Purchase #2	$46.41	8.577%	$50.3906	$50.39	$50.40	$50.40
Purchase #3	$97.90	11.568%	$109.2251	$109.23	$109.25	$109.20
Purchase #4	$145.76	5.498%	$153.7739	$153.77	$153.75	$153.80
Purchase #5	$29.92	12.329%	$33.6088	$33.61	$33.60	$33.60
Purchase #6	$168.84	13.464%	$191.5726	$191.57	$191.55	$191.60
Purchase #7	$38.84	9.269%	$42.4401	$42.44	$42.45	$42.40
7 purchase totals =	$664.17		$726.8832	$726.88	$726.85	$726.90