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	$32.92	4.491%	$34.3984	$34.40	$34.40	$34.40
Purchase #2	$38.85	12.719%	$43.7913	$43.79	$43.80	$43.80
Purchase #3	$132.74	11.487%	$147.9878	$147.99	$148.00	$148.00
Purchase #4	$201.67	13.664%	$229.2262	$229.23	$229.25	$229.20
Purchase #5	$32.48	4.152%	$33.8286	$33.83	$33.85	$33.80
Purchase #6	$78.94	13.428%	$89.5401	$89.54	$89.55	$89.50
Purchase #7	$150.60	13.554%	$171.0123	$171.01	$171.00	$171.00
7 purchase totals =	$668.20		$749.7847	$749.79	$749.85	$749.70