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	$58.53	5.109%	$61.5203	$61.52	$61.50	$61.50
Purchase #2	$209.47	10.520%	$231.5062	$231.51	$231.50	$231.50
Purchase #3	$72.95	13.672%	$82.9237	$82.92	$82.90	$82.90
Purchase #4	$31.67	5.651%	$33.4597	$33.46	$33.45	$33.50
Purchase #5	$248.50	7.496%	$267.1276	$267.13	$267.15	$267.10
Purchase #6	$111.33	6.828%	$118.9316	$118.93	$118.95	$118.90
Purchase #7	$43.84	7.508%	$47.1315	$47.13	$47.15	$47.10
7 purchase totals =	$776.29		$842.6006	$842.60	$842.60	$842.50