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	$208.32	12.217%	$233.7705	$233.77	$233.75	$233.80
Purchase #2	$47.85	6.403%	$50.9138	$50.91	$50.90	$50.90
Purchase #3	$134.96	13.626%	$153.3496	$153.35	$153.35	$153.30
Purchase #4	$139.86	10.838%	$155.018	$155.02	$155.00	$155.00
Purchase #5	$52.59	6.106%	$55.8011	$55.80	$55.80	$55.80
Purchase #6	$128.63	6.554%	$137.0604	$137.06	$137.05	$137.10
Purchase #7	$227.50	12.587%	$256.1354	$256.14	$256.15	$256.10
7 purchase totals =	$939.71		$1,042.0488	$1,042.05	$1,042.00	$1,042.00