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	$100.61	11.115%	$111.7928	$111.79	$111.80	$111.80
Purchase #2	$83.68	6.607%	$89.2087	$89.21	$89.20	$89.20
Purchase #3	$218.62	13.599%	$248.3501	$248.35	$248.35	$248.40
Purchase #4	$217.27	10.611%	$240.3245	$240.32	$240.30	$240.30
Purchase #5	$224.63	3.196%	$231.8092	$231.81	$231.80	$231.80
Purchase #6	$200.47	5.268%	$211.0308	$211.03	$211.05	$211.00
Purchase #7	$137.40	13.700%	$156.2238	$156.22	$156.20	$156.20
7 purchase totals =	$1,182.68		$1,288.7399	$1,288.73	$1,288.70	$1,288.70