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	$248.57	6.548%	$264.8464	$264.85	$264.85	$264.80
Purchase #2	$180.54	3.860%	$187.5088	$187.51	$187.50	$187.50
Purchase #3	$79.78	8.507%	$86.5669	$86.57	$86.55	$86.60
Purchase #4	$178.29	10.309%	$196.6699	$196.67	$196.65	$196.70
Purchase #5	$11.99	12.774%	$13.5216	$13.52	$13.50	$13.50
Purchase #6	$242.34	3.448%	$250.6959	$250.70	$250.70	$250.70
Purchase #7	$84.59	4.245%	$88.1808	$88.18	$88.20	$88.20
7 purchase totals =	$1,026.10		$1,087.9903	$1,088.00	$1,087.95	$1,088.00