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	$45.95	3.371%	$47.499	$47.50	$47.50	$47.50
Purchase #2	$120.31	9.280%	$131.4748	$131.47	$131.45	$131.50
Purchase #3	$74.86	4.699%	$78.3777	$78.38	$78.40	$78.40
Purchase #4	$142.86	4.726%	$149.6116	$149.61	$149.60	$149.60
Purchase #5	$143.91	11.835%	$160.9417	$160.94	$160.95	$160.90
Purchase #6	$163.95	6.614%	$174.7937	$174.79	$174.80	$174.80
Purchase #7	$87.55	3.661%	$90.7552	$90.76	$90.75	$90.80
7 purchase totals =	$779.39		$833.4537	$833.45	$833.45	$833.50