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	$70.59	12.813%	$79.6347	$79.63	$79.65	$79.60
Purchase #2	$100.80	10.569%	$111.4536	$111.45	$111.45	$111.50
Purchase #3	$249.47	12.521%	$280.7061	$280.71	$280.70	$280.70
Purchase #4	$227.28	7.345%	$243.9737	$243.97	$243.95	$244.00
Purchase #5	$67.94	7.288%	$72.8915	$72.89	$72.90	$72.90
Purchase #6	$192.52	7.792%	$207.5212	$207.52	$207.50	$207.50
Purchase #7	$127.48	7.656%	$137.2399	$137.24	$137.25	$137.20
7 purchase totals =	$1,036.08		$1,133.4207	$1,133.41	$1,133.40	$1,133.40