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	$245.49	13.247%	$278.0101	$278.01	$278.00	$278.00
Purchase #2	$90.56	12.122%	$101.5377	$101.54	$101.55	$101.50
Purchase #3	$154.95	7.630%	$166.7727	$166.77	$166.75	$166.80
Purchase #4	$124.72	9.382%	$136.4212	$136.42	$136.40	$136.40
Purchase #5	$152.50	6.484%	$162.3881	$162.39	$162.40	$162.40
Purchase #6	$105.58	3.582%	$109.3619	$109.36	$109.35	$109.40
Purchase #7	$210.80	3.822%	$218.8568	$218.86	$218.85	$218.90
7 purchase totals =	$1,084.60		$1,173.3485	$1,173.35	$1,173.30	$1,173.40