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	$33.54	11.331%	$37.3404	$37.34	$37.35	$37.30
Purchase #2	$72.30	11.266%	$80.4453	$80.45	$80.45	$80.40
Purchase #3	$132.85	7.277%	$142.5175	$142.52	$142.50	$142.50
Purchase #4	$72.94	7.401%	$78.3383	$78.34	$78.35	$78.30
Purchase #5	$101.37	3.836%	$105.2586	$105.26	$105.25	$105.30
Purchase #6	$148.70	4.514%	$155.4123	$155.41	$155.40	$155.40
Purchase #7	$98.30	13.523%	$111.5931	$111.59	$111.60	$111.60
7 purchase totals =	$660.00		$710.9055	$710.91	$710.90	$710.80