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	$229.50	11.398%	$255.6584	$255.66	$255.65	$255.70
Purchase #2	$156.63	10.148%	$172.5248	$172.52	$172.50	$172.50
Purchase #3	$127.94	12.709%	$144.1999	$144.20	$144.20	$144.20
Purchase #4	$156.40	4.481%	$163.4083	$163.41	$163.40	$163.40
Purchase #5	$89.79	9.305%	$98.145	$98.15	$98.15	$98.10
Purchase #6	$101.84	3.146%	$105.0439	$105.04	$105.05	$105.00
Purchase #7	$131.69	8.452%	$142.8204	$142.82	$142.80	$142.80
7 purchase totals =	$993.79		$1,081.8007	$1,081.80	$1,081.75	$1,081.70