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	$93.64	12.266%	$105.1259	$105.13	$105.15	$105.10
Purchase #2	$233.63	9.375%	$255.5328	$255.53	$255.55	$255.50
Purchase #3	$102.72	9.509%	$112.4876	$112.49	$112.50	$112.50
Purchase #4	$50.73	13.580%	$57.6191	$57.62	$57.60	$57.60
Purchase #5	$145.59	13.648%	$165.4601	$165.46	$165.45	$165.50
Purchase #6	$37.83	12.809%	$42.6756	$42.68	$42.70	$42.70
Purchase #7	$150.96	12.328%	$169.5703	$169.57	$169.55	$169.60
7 purchase totals =	$815.10		$908.4714	$908.48	$908.50	$908.50