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	$155.76	13.400%	$176.6318	$176.63	$176.65	$176.60
Purchase #2	$55.66	3.274%	$57.4823	$57.48	$57.50	$57.50
Purchase #3	$61.58	10.377%	$67.9702	$67.97	$67.95	$68.00
Purchase #4	$40.66	3.564%	$42.1091	$42.11	$42.10	$42.10
Purchase #5	$249.86	9.502%	$273.6017	$273.60	$273.60	$273.60
Purchase #6	$37.41	7.664%	$40.2771	$40.28	$40.30	$40.30
Purchase #7	$205.45	10.822%	$227.6838	$227.68	$227.70	$227.70
7 purchase totals =	$806.38		$885.7560	$885.75	$885.80	$885.80