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	$249.99	4.221%	$260.5421	$260.54	$260.55	$260.50
Purchase #2	$108.26	10.342%	$119.4562	$119.46	$119.45	$119.50
Purchase #3	$19.58	4.697%	$20.4997	$20.50	$20.50	$20.50
Purchase #4	$96.89	3.534%	$100.3141	$100.31	$100.30	$100.30
Purchase #5	$182.44	12.649%	$205.5168	$205.52	$205.50	$205.50
Purchase #6	$149.58	13.154%	$169.2558	$169.26	$169.25	$169.30
Purchase #7	$42.36	7.541%	$45.5544	$45.55	$45.55	$45.60
7 purchase totals =	$849.10		$921.1391	$921.14	$921.10	$921.20