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	$103.82	6.236%	$110.2942	$110.29	$110.30	$110.30
Purchase #2	$57.81	6.358%	$61.4856	$61.49	$61.50	$61.50
Purchase #3	$177.96	12.563%	$200.3171	$200.32	$200.30	$200.30
Purchase #4	$177.83	12.688%	$200.3931	$200.39	$200.40	$200.40
Purchase #5	$150.83	8.551%	$163.7275	$163.73	$163.75	$163.70
Purchase #6	$196.45	8.226%	$212.61	$212.61	$212.60	$212.60
Purchase #7	$140.55	7.224%	$150.7033	$150.70	$150.70	$150.70
7 purchase totals =	$1,005.25		$1,099.5308	$1,099.53	$1,099.55	$1,099.50