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	$239.77	13.530%	$272.2109	$272.21	$272.20	$272.20
Purchase #2	$76.31	8.669%	$82.9253	$82.93	$82.95	$82.90
Purchase #3	$19.96	6.413%	$21.24	$21.24	$21.25	$21.20
Purchase #4	$210.32	5.713%	$222.3356	$222.34	$222.35	$222.30
Purchase #5	$70.59	4.840%	$74.0066	$74.01	$74.00	$74.00
Purchase #6	$35.70	4.832%	$37.425	$37.43	$37.45	$37.40
Purchase #7	$54.28	3.281%	$56.0609	$56.06	$56.05	$56.10
7 purchase totals =	$706.93		$766.2043	$766.22	$766.25	$766.10