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	$150.67	13.440%	$170.92	$170.92	$170.90	$170.90
Purchase #2	$39.95	7.330%	$42.8783	$42.88	$42.90	$42.90
Purchase #3	$228.49	13.557%	$259.4664	$259.47	$259.45	$259.50
Purchase #4	$144.34	12.285%	$162.0722	$162.07	$162.05	$162.10
Purchase #5	$44.78	10.342%	$49.4111	$49.41	$49.40	$49.40
Purchase #6	$161.54	3.127%	$166.5914	$166.59	$166.60	$166.60
Purchase #7	$159.28	12.308%	$178.8842	$178.88	$178.90	$178.90
7 purchase totals =	$929.05		$1,030.2236	$1,030.22	$1,030.20	$1,030.30