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	$154.61	8.591%	$167.8925	$167.89	$167.90	$167.90
Purchase #2	$79.89	13.764%	$90.8861	$90.89	$90.90	$90.90
Purchase #3	$233.34	7.387%	$250.5768	$250.58	$250.60	$250.60
Purchase #4	$56.80	3.567%	$58.8261	$58.83	$58.85	$58.80
Purchase #5	$203.87	12.770%	$229.9042	$229.90	$229.90	$229.90
Purchase #6	$181.92	12.321%	$204.3344	$204.33	$204.35	$204.30
Purchase #7	$199.37	4.577%	$208.4952	$208.50	$208.50	$208.50
7 purchase totals =	$1,109.80		$1,210.9153	$1,210.92	$1,211.00	$1,210.90