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	$109.75	10.679%	$121.4702	$121.47	$121.45	$121.50
Purchase #2	$39.50	6.550%	$42.0873	$42.09	$42.10	$42.10
Purchase #3	$241.97	4.816%	$253.6233	$253.62	$253.60	$253.60
Purchase #4	$200.43	5.149%	$210.7501	$210.75	$210.75	$210.80
Purchase #5	$131.57	12.327%	$147.7886	$147.79	$147.80	$147.80
Purchase #6	$38.41	11.572%	$42.8548	$42.85	$42.85	$42.90
Purchase #7	$32.89	8.113%	$35.5584	$35.56	$35.55	$35.60
7 purchase totals =	$794.52		$854.1327	$854.13	$854.10	$854.30