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	$79.82	6.607%	$85.0937	$85.09	$85.10	$85.10
Purchase #2	$105.42	13.238%	$119.3755	$119.38	$119.40	$119.40
Purchase #3	$137.55	4.712%	$144.0314	$144.03	$144.05	$144.00
Purchase #4	$168.30	13.493%	$191.0087	$191.01	$191.00	$191.00
Purchase #5	$69.32	4.316%	$72.3119	$72.31	$72.30	$72.30
Purchase #6	$139.57	11.732%	$155.9444	$155.94	$155.95	$155.90
Purchase #7	$197.91	7.546%	$212.8443	$212.84	$212.85	$212.80
7 purchase totals =	$897.89		$980.6099	$980.60	$980.65	$980.50