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	$57.91	6.126%	$61.4576	$61.46	$61.45	$61.50
Purchase #2	$137.29	12.737%	$154.7766	$154.78	$154.80	$154.80
Purchase #3	$156.78	4.689%	$164.1314	$164.13	$164.15	$164.10
Purchase #4	$39.94	7.122%	$42.7845	$42.78	$42.80	$42.80
Purchase #5	$28.31	11.597%	$31.5931	$31.59	$31.60	$31.60
Purchase #6	$163.79	4.589%	$171.3063	$171.31	$171.30	$171.30
Purchase #7	$80.78	13.627%	$91.7879	$91.79	$91.80	$91.80
7 purchase totals =	$664.80		$717.8374	$717.84	$717.90	$717.90