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	$226.51	10.762%	$250.887	$250.89	$250.90	$250.90
Purchase #2	$143.31	11.102%	$159.2203	$159.22	$159.20	$159.20
Purchase #3	$101.27	12.406%	$113.8336	$113.83	$113.85	$113.80
Purchase #4	$49.38	10.139%	$54.3866	$54.39	$54.40	$54.40
Purchase #5	$31.52	13.828%	$35.8786	$35.88	$35.90	$35.90
Purchase #6	$150.30	4.807%	$157.5249	$157.52	$157.50	$157.50
Purchase #7	$34.53	12.638%	$38.8939	$38.89	$38.90	$38.90
7 purchase totals =	$736.82		$810.6249	$810.62	$810.65	$810.60