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	$127.98	8.743%	$139.1693	$139.17	$139.15	$139.20
Purchase #2	$92.72	8.291%	$100.4074	$100.41	$100.40	$100.40
Purchase #3	$193.74	10.144%	$213.393	$213.39	$213.40	$213.40
Purchase #4	$91.52	5.507%	$96.56	$96.56	$96.55	$96.60
Purchase #5	$206.85	9.857%	$227.2392	$227.24	$227.25	$227.20
Purchase #6	$41.62	6.671%	$44.3965	$44.40	$44.40	$44.40
Purchase #7	$151.61	8.466%	$164.4453	$164.45	$164.45	$164.40
7 purchase totals =	$906.04		$985.6107	$985.62	$985.60	$985.60