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	$90.43	11.369%	$100.711	$100.71	$100.70	$100.70
Purchase #2	$35.63	3.520%	$36.8842	$36.88	$36.90	$36.90
Purchase #3	$140.42	4.473%	$146.701	$146.70	$146.70	$146.70
Purchase #4	$112.89	6.669%	$120.4186	$120.42	$120.40	$120.40
Purchase #5	$182.87	9.706%	$200.6194	$200.62	$200.60	$200.60
Purchase #6	$111.39	9.370%	$121.8272	$121.83	$121.85	$121.80
Purchase #7	$106.28	5.803%	$112.4474	$112.45	$112.45	$112.40
7 purchase totals =	$779.91		$839.6088	$839.61	$839.60	$839.50