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	$37.66	13.289%	$42.6646	$42.66	$42.65	$42.70
Purchase #2	$50.42	3.845%	$52.3586	$52.36	$52.35	$52.40
Purchase #3	$35.40	4.653%	$37.0472	$37.05	$37.05	$37.00
Purchase #4	$227.78	4.500%	$238.0301	$238.03	$238.05	$238.00
Purchase #5	$120.94	11.164%	$134.4417	$134.44	$134.45	$134.40
Purchase #6	$188.36	10.739%	$208.588	$208.59	$208.60	$208.60
Purchase #7	$149.92	4.477%	$156.6319	$156.63	$156.65	$156.60
7 purchase totals =	$810.48		$869.7621	$869.76	$869.80	$869.70