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	$178.45	4.322%	$186.1626	$186.16	$186.15	$186.20
Purchase #2	$32.44	9.512%	$35.5257	$35.53	$35.55	$35.50
Purchase #3	$81.67	4.265%	$85.1532	$85.15	$85.15	$85.20
Purchase #4	$164.64	10.834%	$182.4771	$182.48	$182.50	$182.50
Purchase #5	$76.91	8.678%	$83.5842	$83.58	$83.60	$83.60
Purchase #6	$80.62	3.256%	$83.245	$83.25	$83.25	$83.20
Purchase #7	$144.40	9.855%	$158.6306	$158.63	$158.65	$158.60
7 purchase totals =	$759.13		$814.7784	$814.78	$814.85	$814.80