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	$123.77	5.851%	$131.0118	$131.01	$131.00	$131.00
Purchase #2	$123.39	6.645%	$131.5893	$131.59	$131.60	$131.60
Purchase #3	$153.56	9.105%	$167.5416	$167.54	$167.55	$167.50
Purchase #4	$220.96	5.107%	$232.2444	$232.24	$232.25	$232.20
Purchase #5	$37.91	13.502%	$43.0286	$43.03	$43.05	$43.00
Purchase #6	$43.28	3.316%	$44.7152	$44.72	$44.70	$44.70
Purchase #7	$127.92	11.439%	$142.5528	$142.55	$142.55	$142.60
7 purchase totals =	$830.79		$892.6837	$892.68	$892.70	$892.60