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	$46.52	8.207%	$50.3379	$50.34	$50.35	$50.30
Purchase #2	$128.25	10.642%	$141.8984	$141.90	$141.90	$141.90
Purchase #3	$29.53	7.572%	$31.766	$31.77	$31.75	$31.80
Purchase #4	$244.45	6.130%	$259.4348	$259.43	$259.45	$259.40
Purchase #5	$176.64	3.864%	$183.4654	$183.47	$183.45	$183.50
Purchase #6	$219.64	4.151%	$228.7573	$228.76	$228.75	$228.80
Purchase #7	$168.64	9.386%	$184.4686	$184.47	$184.45	$184.50
7 purchase totals =	$1,013.67		$1,080.1284	$1,080.14	$1,080.10	$1,080.20