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	$34.25	9.805%	$37.6082	$37.61	$37.60	$37.60
Purchase #2	$132.47	12.242%	$148.687	$148.69	$148.70	$148.70
Purchase #3	$100.67	10.667%	$111.4085	$111.41	$111.40	$111.40
Purchase #4	$168.46	13.396%	$191.0269	$191.03	$191.05	$191.00
Purchase #5	$132.97	8.259%	$143.952	$143.95	$143.95	$144.00
Purchase #6	$162.95	3.461%	$168.5897	$168.59	$168.60	$168.60
Purchase #7	$164.55	3.850%	$170.8852	$170.89	$170.90	$170.90
7 purchase totals =	$896.32		$972.1575	$972.17	$972.20	$972.20