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	$246.56	4.851%	$258.5206	$258.52	$258.50	$258.50
Purchase #2	$92.61	7.357%	$99.4233	$99.42	$99.40	$99.40
Purchase #3	$171.38	9.546%	$187.7399	$187.74	$187.75	$187.70
Purchase #4	$49.67	3.300%	$51.3091	$51.31	$51.30	$51.30
Purchase #5	$128.25	10.671%	$141.9356	$141.94	$141.95	$141.90
Purchase #6	$216.94	11.721%	$242.3675	$242.37	$242.35	$242.40
Purchase #7	$41.84	4.412%	$43.686	$43.69	$43.70	$43.70
7 purchase totals =	$947.25		$1,024.9820	$1,024.99	$1,024.95	$1,024.90