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	$242.52	8.801%	$263.8642	$263.86	$263.85	$263.90
Purchase #2	$233.44	13.580%	$265.1412	$265.14	$265.15	$265.10
Purchase #3	$14.44	11.816%	$16.1462	$16.15	$16.15	$16.10
Purchase #4	$36.58	12.485%	$41.147	$41.15	$41.15	$41.10
Purchase #5	$139.59	7.839%	$150.5325	$150.53	$150.55	$150.50
Purchase #6	$190.50	13.650%	$216.5033	$216.50	$216.50	$216.50
Purchase #7	$44.93	3.648%	$46.569	$46.57	$46.55	$46.60
7 purchase totals =	$902.00		$999.9034	$999.90	$999.90	$999.80