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	$28.76	10.501%	$31.7801	$31.78	$31.80	$31.80
Purchase #2	$131.53	8.713%	$142.9902	$142.99	$143.00	$143.00
Purchase #3	$196.96	13.464%	$223.4787	$223.48	$223.50	$223.50
Purchase #4	$188.97	5.866%	$200.055	$200.06	$200.05	$200.10
Purchase #5	$28.54	12.182%	$32.0167	$32.02	$32.00	$32.00
Purchase #6	$139.61	3.814%	$144.9347	$144.93	$144.95	$144.90
Purchase #7	$60.80	3.449%	$62.897	$62.90	$62.90	$62.90
7 purchase totals =	$775.17		$838.1524	$838.16	$838.20	$838.20