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	$108.96	13.326%	$123.48	$123.48	$123.50	$123.50
Purchase #2	$40.78	3.653%	$42.2697	$42.27	$42.25	$42.30
Purchase #3	$238.78	12.449%	$268.5057	$268.51	$268.50	$268.50
Purchase #4	$91.34	3.725%	$94.7424	$94.74	$94.75	$94.70
Purchase #5	$189.71	13.419%	$215.1672	$215.17	$215.15	$215.20
Purchase #6	$212.82	8.509%	$230.9289	$230.93	$230.95	$230.90
Purchase #7	$87.61	4.129%	$91.2274	$91.23	$91.25	$91.20
7 purchase totals =	$970.00		$1,066.3213	$1,066.33	$1,066.35	$1,066.30