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	$233.93	6.161%	$248.3424	$248.34	$248.35	$248.30
Purchase #2	$149.36	11.629%	$166.7291	$166.73	$166.75	$166.70
Purchase #3	$233.42	7.459%	$250.8308	$250.83	$250.85	$250.80
Purchase #4	$114.59	3.171%	$118.2236	$118.22	$118.20	$118.20
Purchase #5	$171.61	9.260%	$187.5011	$187.50	$187.50	$187.50
Purchase #6	$126.53	10.532%	$139.8561	$139.86	$139.85	$139.90
Purchase #7	$113.39	7.389%	$121.7684	$121.77	$121.75	$121.80
7 purchase totals =	$1,142.83		$1,233.2515	$1,233.25	$1,233.25	$1,233.20