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	$199.69	6.301%	$212.2725	$212.27	$212.25	$212.30
Purchase #2	$143.87	10.468%	$158.9303	$158.93	$158.95	$158.90
Purchase #3	$115.61	10.612%	$127.8785	$127.88	$127.90	$127.90
Purchase #4	$27.72	5.263%	$29.1789	$29.18	$29.20	$29.20
Purchase #5	$138.31	6.480%	$147.2725	$147.27	$147.25	$147.30
Purchase #6	$75.99	13.353%	$86.1369	$86.14	$86.15	$86.10
Purchase #7	$214.36	4.565%	$224.1455	$224.15	$224.15	$224.10
7 purchase totals =	$915.55		$985.8151	$985.82	$985.85	$985.80