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	$178.47	6.379%	$189.8546	$189.85	$189.85	$189.90
Purchase #2	$219.69	7.708%	$236.6237	$236.62	$236.60	$236.60
Purchase #3	$135.55	3.273%	$139.9866	$139.99	$140.00	$140.00
Purchase #4	$36.41	4.706%	$38.1235	$38.12	$38.10	$38.10
Purchase #5	$213.25	11.753%	$238.3133	$238.31	$238.30	$238.30
Purchase #6	$134.62	13.257%	$152.4666	$152.47	$152.45	$152.50
Purchase #7	$147.71	5.326%	$155.577	$155.58	$155.60	$155.60
7 purchase totals =	$1,065.70		$1,150.9453	$1,150.94	$1,150.90	$1,151.00