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	$31.52	4.772%	$33.0241	$33.02	$33.00	$33.00
Purchase #2	$50.94	9.193%	$55.6229	$55.62	$55.60	$55.60
Purchase #3	$34.99	4.198%	$36.4589	$36.46	$36.45	$36.50
Purchase #4	$220.70	9.805%	$242.3396	$242.34	$242.35	$242.30
Purchase #5	$154.92	6.186%	$164.5034	$164.50	$164.50	$164.50
Purchase #6	$41.81	4.256%	$43.5894	$43.59	$43.60	$43.60
Purchase #7	$240.40	9.760%	$263.863	$263.86	$263.85	$263.90
7 purchase totals =	$775.28		$839.4013	$839.39	$839.35	$839.40