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	$237.82	5.277%	$250.3698	$250.37	$250.35	$250.40
Purchase #2	$229.40	12.831%	$258.8343	$258.83	$258.85	$258.80
Purchase #3	$100.32	11.512%	$111.8688	$111.87	$111.85	$111.90
Purchase #4	$176.87	6.453%	$188.2834	$188.28	$188.30	$188.30
Purchase #5	$41.77	3.704%	$43.3172	$43.32	$43.30	$43.30
Purchase #6	$216.64	9.782%	$237.8317	$237.83	$237.85	$237.80
Purchase #7	$229.58	13.684%	$260.9957	$261.00	$261.00	$261.00
7 purchase totals =	$1,232.40		$1,351.5009	$1,351.50	$1,351.50	$1,351.50