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	$42.57	13.233%	$48.2033	$48.20	$48.20	$48.20
Purchase #2	$192.46	13.363%	$218.1784	$218.18	$218.20	$218.20
Purchase #3	$220.67	5.758%	$233.3762	$233.38	$233.40	$233.40
Purchase #4	$151.58	8.738%	$164.8251	$164.83	$164.85	$164.80
Purchase #5	$141.89	12.749%	$159.9796	$159.98	$160.00	$160.00
Purchase #6	$139.52	13.478%	$158.3245	$158.32	$158.30	$158.30
Purchase #7	$91.83	6.731%	$98.0111	$98.01	$98.00	$98.00
7 purchase totals =	$980.52		$1,080.8982	$1,080.90	$1,080.95	$1,080.90