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	$14.38	9.290%	$15.7159	$15.72	$15.70	$15.70
Purchase #2	$179.77	11.494%	$200.4328	$200.43	$200.45	$200.40
Purchase #3	$190.51	13.541%	$216.307	$216.31	$216.30	$216.30
Purchase #4	$232.50	11.562%	$259.3817	$259.38	$259.40	$259.40
Purchase #5	$165.67	9.779%	$181.8709	$181.87	$181.85	$181.90
Purchase #6	$45.51	5.557%	$48.039	$48.04	$48.05	$48.00
Purchase #7	$140.95	12.810%	$159.0057	$159.01	$159.00	$159.00
7 purchase totals =	$969.29		$1,080.7530	$1,080.76	$1,080.75	$1,080.70