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	$147.33	11.708%	$164.5794	$164.58	$164.60	$164.60
Purchase #2	$27.72	3.406%	$28.6641	$28.66	$28.65	$28.70
Purchase #3	$108.97	10.253%	$120.1427	$120.14	$120.15	$120.10
Purchase #4	$52.82	13.397%	$59.8963	$59.90	$59.90	$59.90
Purchase #5	$188.26	13.338%	$213.3701	$213.37	$213.35	$213.40
Purchase #6	$49.88	8.278%	$54.0091	$54.01	$54.00	$54.00
Purchase #7	$34.35	6.268%	$36.5031	$36.50	$36.50	$36.50
7 purchase totals =	$609.33		$677.1648	$677.16	$677.15	$677.20