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	$34.72	5.484%	$36.624	$36.62	$36.60	$36.60
Purchase #2	$65.74	10.485%	$72.6328	$72.63	$72.65	$72.60
Purchase #3	$85.67	9.767%	$94.0374	$94.04	$94.05	$94.00
Purchase #4	$245.79	8.535%	$266.7682	$266.77	$266.75	$266.80
Purchase #5	$88.50	3.838%	$91.8966	$91.90	$91.90	$91.90
Purchase #6	$16.79	3.230%	$17.3323	$17.33	$17.35	$17.30
Purchase #7	$80.68	12.372%	$90.6617	$90.66	$90.65	$90.70
7 purchase totals =	$617.89		$669.9530	$669.95	$669.95	$669.90