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	$44.47	13.487%	$50.4677	$50.47	$50.45	$50.50
Purchase #2	$54.46	8.809%	$59.2574	$59.26	$59.25	$59.30
Purchase #3	$242.75	10.601%	$268.4839	$268.48	$268.50	$268.50
Purchase #4	$97.61	7.285%	$104.7209	$104.72	$104.70	$104.70
Purchase #5	$249.93	4.146%	$260.2921	$260.29	$260.30	$260.30
Purchase #6	$246.93	10.302%	$272.3687	$272.37	$272.35	$272.40
Purchase #7	$179.95	11.133%	$199.9838	$199.98	$200.00	$200.00
7 purchase totals =	$1,116.10		$1,215.5745	$1,215.57	$1,215.55	$1,215.70