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	$126.89	7.759%	$136.7354	$136.74	$136.75	$136.70
Purchase #2	$89.66	4.123%	$93.3567	$93.36	$93.35	$93.40
Purchase #3	$146.32	13.339%	$165.8376	$165.84	$165.85	$165.80
Purchase #4	$131.50	10.590%	$145.4259	$145.43	$145.45	$145.40
Purchase #5	$233.97	12.102%	$262.285	$262.29	$262.30	$262.30
Purchase #6	$86.53	10.323%	$95.4625	$95.46	$95.45	$95.50
Purchase #7	$123.34	13.256%	$139.69	$139.69	$139.70	$139.70
7 purchase totals =	$938.21		$1,038.7931	$1,038.81	$1,038.85	$1,038.80