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	$25.85	9.769%	$28.3753	$28.38	$28.40	$28.40
Purchase #2	$24.77	11.211%	$27.547	$27.55	$27.55	$27.50
Purchase #3	$70.81	4.340%	$73.8832	$73.88	$73.90	$73.90
Purchase #4	$209.52	10.643%	$231.8192	$231.82	$231.80	$231.80
Purchase #5	$144.79	13.349%	$164.118	$164.12	$164.10	$164.10
Purchase #6	$226.90	7.272%	$243.4002	$243.40	$243.40	$243.40
Purchase #7	$192.88	9.853%	$211.8845	$211.88	$211.90	$211.90
7 purchase totals =	$895.52		$981.0274	$981.03	$981.05	$981.00