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	$28.78	12.527%	$32.3853	$32.39	$32.40	$32.40
Purchase #2	$61.71	8.223%	$66.7844	$66.78	$66.80	$66.80
Purchase #3	$78.75	10.244%	$86.8172	$86.82	$86.80	$86.80
Purchase #4	$82.52	3.638%	$85.5221	$85.52	$85.50	$85.50
Purchase #5	$170.61	6.612%	$181.8907	$181.89	$181.90	$181.90
Purchase #6	$126.44	5.258%	$133.0882	$133.09	$133.10	$133.10
Purchase #7	$118.80	9.787%	$130.427	$130.43	$130.45	$130.40
7 purchase totals =	$667.61		$716.9149	$716.92	$716.95	$716.90