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	$121.69	6.251%	$129.2968	$129.30	$129.30	$129.30
Purchase #2	$230.85	10.687%	$255.5209	$255.52	$255.50	$255.50
Purchase #3	$75.98	8.558%	$82.4824	$82.48	$82.50	$82.50
Purchase #4	$82.53	9.659%	$90.5016	$90.50	$90.50	$90.50
Purchase #5	$200.42	4.119%	$208.6753	$208.68	$208.70	$208.70
Purchase #6	$47.98	8.159%	$51.8947	$51.89	$51.90	$51.90
Purchase #7	$207.82	12.753%	$234.3233	$234.32	$234.30	$234.30
7 purchase totals =	$967.27		$1,052.6950	$1,052.69	$1,052.70	$1,052.70