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	$111.71	12.682%	$125.8771	$125.88	$125.90	$125.90
Purchase #2	$111.36	13.675%	$126.5885	$126.59	$126.60	$126.60
Purchase #3	$98.51	7.393%	$105.7928	$105.79	$105.80	$105.80
Purchase #4	$245.61	13.847%	$279.6196	$279.62	$279.60	$279.60
Purchase #5	$135.64	5.360%	$142.9103	$142.91	$142.90	$142.90
Purchase #6	$228.32	13.617%	$259.4103	$259.41	$259.40	$259.40
Purchase #7	$38.88	4.790%	$40.7424	$40.74	$40.75	$40.70
7 purchase totals =	$970.03		$1,080.9410	$1,080.94	$1,080.95	$1,080.90