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	$206.44	11.579%	$230.3437	$230.34	$230.35	$230.30
Purchase #2	$40.77	6.647%	$43.48	$43.48	$43.50	$43.50
Purchase #3	$240.34	12.250%	$269.7817	$269.78	$269.80	$269.80
Purchase #4	$90.89	10.264%	$100.2189	$100.22	$100.20	$100.20
Purchase #5	$85.30	6.201%	$90.5895	$90.59	$90.60	$90.60
Purchase #6	$187.91	7.411%	$201.836	$201.84	$201.85	$201.80
Purchase #7	$62.75	6.547%	$66.8582	$66.86	$66.85	$66.90
7 purchase totals =	$914.40		$1,003.1080	$1,003.11	$1,003.15	$1,003.10