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	$247.97	10.258%	$273.4068	$273.41	$273.40	$273.40
Purchase #2	$97.26	11.861%	$108.796	$108.80	$108.80	$108.80
Purchase #3	$134.86	5.517%	$142.3002	$142.30	$142.30	$142.30
Purchase #4	$150.68	12.795%	$169.9595	$169.96	$169.95	$170.00
Purchase #5	$66.60	7.420%	$71.5417	$71.54	$71.55	$71.50
Purchase #6	$44.53	8.533%	$48.3297	$48.33	$48.35	$48.30
Purchase #7	$118.71	4.382%	$123.9119	$123.91	$123.90	$123.90
7 purchase totals =	$860.61		$938.2458	$938.25	$938.25	$938.20