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	$160.58	4.688%	$168.108	$168.11	$168.10	$168.10
Purchase #2	$248.26	6.762%	$265.0473	$265.05	$265.05	$265.00
Purchase #3	$226.53	12.493%	$254.8304	$254.83	$254.85	$254.80
Purchase #4	$98.63	13.191%	$111.6403	$111.64	$111.65	$111.60
Purchase #5	$176.58	11.464%	$196.8231	$196.82	$196.80	$196.80
Purchase #6	$18.29	7.715%	$19.7011	$19.70	$19.70	$19.70
Purchase #7	$13.63	6.254%	$14.4824	$14.48	$14.50	$14.50
7 purchase totals =	$942.50		$1,030.6326	$1,030.63	$1,030.65	$1,030.50