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	$6.29	11.112%	$6.9889	$6.99	$7.00	$7.00
Purchase #2	$217.65	9.381%	$238.0677	$238.07	$238.05	$238.10
Purchase #3	$144.89	4.637%	$151.6085	$151.61	$151.60	$151.60
Purchase #4	$103.52	7.554%	$111.3399	$111.34	$111.35	$111.30
Purchase #5	$27.63	4.819%	$28.9615	$28.96	$28.95	$29.00
Purchase #6	$168.57	13.322%	$191.0269	$191.03	$191.05	$191.00
Purchase #7	$184.58	8.529%	$200.3228	$200.32	$200.30	$200.30
7 purchase totals =	$853.13		$928.3162	$928.32	$928.30	$928.30