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	$247.77	10.792%	$274.5093	$274.51	$274.50	$274.50
Purchase #2	$100.34	7.158%	$107.5223	$107.52	$107.50	$107.50
Purchase #3	$127.40	7.395%	$136.8212	$136.82	$136.80	$136.80
Purchase #4	$81.58	9.295%	$89.1629	$89.16	$89.15	$89.20
Purchase #5	$41.46	10.721%	$45.9049	$45.90	$45.90	$45.90
Purchase #6	$51.48	9.204%	$56.2182	$56.22	$56.20	$56.20
Purchase #7	$94.51	4.466%	$98.7308	$98.73	$98.75	$98.70
7 purchase totals =	$744.54		$808.8696	$808.86	$808.80	$808.80