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	$86.40	3.622%	$89.5294	$89.53	$89.55	$89.50
Purchase #2	$102.72	8.347%	$111.294	$111.29	$111.30	$111.30
Purchase #3	$244.33	4.437%	$255.1709	$255.17	$255.15	$255.20
Purchase #4	$40.26	7.276%	$43.1893	$43.19	$43.20	$43.20
Purchase #5	$107.50	5.744%	$113.6748	$113.67	$113.65	$113.70
Purchase #6	$97.29	13.635%	$110.5555	$110.56	$110.55	$110.60
Purchase #7	$163.41	11.574%	$182.3231	$182.32	$182.30	$182.30
7 purchase totals =	$841.91		$905.7370	$905.73	$905.70	$905.80