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	$32.91	8.791%	$35.8031	$35.80	$35.80	$35.80
Purchase #2	$227.54	5.535%	$240.1343	$240.13	$240.15	$240.10
Purchase #3	$227.39	3.744%	$235.9035	$235.90	$235.90	$235.90
Purchase #4	$212.50	12.160%	$238.34	$238.34	$238.35	$238.30
Purchase #5	$43.28	4.800%	$45.3574	$45.36	$45.35	$45.40
Purchase #6	$158.69	7.816%	$171.0932	$171.09	$171.10	$171.10
Purchase #7	$44.44	9.634%	$48.7213	$48.72	$48.70	$48.70
7 purchase totals =	$946.75		$1,015.3528	$1,015.34	$1,015.35	$1,015.30