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	$55.92	9.261%	$61.0988	$61.10	$61.10	$61.10
Purchase #2	$39.80	5.659%	$42.0523	$42.05	$42.05	$42.10
Purchase #3	$102.38	9.128%	$111.7252	$111.73	$111.75	$111.70
Purchase #4	$118.61	11.238%	$131.9394	$131.94	$131.95	$131.90
Purchase #5	$117.57	5.798%	$124.3867	$124.39	$124.40	$124.40
Purchase #6	$42.68	11.547%	$47.6083	$47.61	$47.60	$47.60
Purchase #7	$30.77	12.588%	$34.6433	$34.64	$34.65	$34.60
7 purchase totals =	$507.73		$553.4540	$553.46	$553.50	$553.40