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	$132.94	13.127%	$150.391	$150.39	$150.40	$150.40
Purchase #2	$86.75	3.871%	$90.1081	$90.11	$90.10	$90.10
Purchase #3	$59.97	10.137%	$66.0492	$66.05	$66.05	$66.00
Purchase #4	$239.80	11.217%	$266.6984	$266.70	$266.70	$266.70
Purchase #5	$20.41	7.182%	$21.8758	$21.88	$21.90	$21.90
Purchase #6	$98.85	7.190%	$105.9573	$105.96	$105.95	$106.00
Purchase #7	$50.25	3.834%	$52.1766	$52.18	$52.20	$52.20
7 purchase totals =	$688.97		$753.2564	$753.27	$753.30	$753.30