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	$86.91	13.341%	$98.5047	$98.50	$98.50	$98.50
Purchase #2	$18.61	10.688%	$20.599	$20.60	$20.60	$20.60
Purchase #3	$225.28	7.228%	$241.5632	$241.56	$241.55	$241.60
Purchase #4	$54.73	7.741%	$58.9666	$58.97	$58.95	$59.00
Purchase #5	$5.89	11.175%	$6.5482	$6.55	$6.55	$6.50
Purchase #6	$176.36	13.675%	$200.4772	$200.48	$200.50	$200.50
Purchase #7	$137.86	5.244%	$145.0894	$145.09	$145.10	$145.10
7 purchase totals =	$705.64		$771.7483	$771.75	$771.75	$771.80