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	$137.69	4.106%	$143.3436	$143.34	$143.35	$143.30
Purchase #2	$112.55	9.825%	$123.608	$123.61	$123.60	$123.60
Purchase #3	$20.62	6.232%	$21.905	$21.91	$21.90	$21.90
Purchase #4	$132.72	7.460%	$142.6209	$142.62	$142.60	$142.60
Purchase #5	$226.28	7.604%	$243.4863	$243.49	$243.50	$243.50
Purchase #6	$46.35	13.188%	$52.4626	$52.46	$52.45	$52.50
Purchase #7	$102.38	11.144%	$113.7892	$113.79	$113.80	$113.80
7 purchase totals =	$778.59		$841.2156	$841.22	$841.20	$841.20