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	$187.94	11.288%	$209.1547	$209.15	$209.15	$209.20
Purchase #2	$80.45	10.250%	$88.6961	$88.70	$88.70	$88.70
Purchase #3	$123.90	12.303%	$139.1434	$139.14	$139.15	$139.10
Purchase #4	$20.62	3.495%	$21.3407	$21.34	$21.35	$21.30
Purchase #5	$139.81	11.639%	$156.0825	$156.08	$156.10	$156.10
Purchase #6	$88.36	12.709%	$99.5897	$99.59	$99.60	$99.60
Purchase #7	$146.84	5.726%	$155.2481	$155.25	$155.25	$155.20
7 purchase totals =	$787.92		$869.2552	$869.25	$869.30	$869.20