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	$65.88	5.466%	$69.481	$69.48	$69.50	$69.50
Purchase #2	$91.32	9.776%	$100.2474	$100.25	$100.25	$100.20
Purchase #3	$75.45	3.622%	$78.1828	$78.18	$78.20	$78.20
Purchase #4	$166.84	7.535%	$179.4114	$179.41	$179.40	$179.40
Purchase #5	$128.42	11.790%	$143.5607	$143.56	$143.55	$143.60
Purchase #6	$144.75	4.181%	$150.802	$150.80	$150.80	$150.80
Purchase #7	$171.34	8.842%	$186.4899	$186.49	$186.50	$186.50
7 purchase totals =	$844.00		$908.1752	$908.17	$908.20	$908.20