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	$111.76	7.171%	$119.7743	$119.77	$119.75	$119.80
Purchase #2	$246.76	13.107%	$279.1028	$279.10	$279.10	$279.10
Purchase #3	$97.48	10.659%	$107.8704	$107.87	$107.85	$107.90
Purchase #4	$77.37	13.869%	$88.1004	$88.10	$88.10	$88.10
Purchase #5	$174.48	12.493%	$196.2778	$196.28	$196.30	$196.30
Purchase #6	$135.70	5.293%	$142.8826	$142.88	$142.90	$142.90
Purchase #7	$144.85	6.478%	$154.2334	$154.23	$154.25	$154.20
7 purchase totals =	$988.40		$1,088.2417	$1,088.23	$1,088.25	$1,088.30