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	$139.67	6.272%	$148.4301	$148.43	$148.45	$148.40
Purchase #2	$19.65	10.586%	$21.7301	$21.73	$21.75	$21.70
Purchase #3	$40.57	9.750%	$44.5256	$44.53	$44.55	$44.50
Purchase #4	$95.74	7.820%	$103.2269	$103.23	$103.25	$103.20
Purchase #5	$234.49	12.411%	$263.5926	$263.59	$263.60	$263.60
Purchase #6	$108.52	3.752%	$112.5917	$112.59	$112.60	$112.60
Purchase #7	$218.75	10.801%	$242.3772	$242.38	$242.40	$242.40
7 purchase totals =	$857.39		$936.4742	$936.48	$936.60	$936.40