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	$123.45	10.370%	$136.2518	$136.25	$136.25	$136.30
Purchase #2	$77.45	7.411%	$83.1898	$83.19	$83.20	$83.20
Purchase #3	$16.75	11.593%	$18.6918	$18.69	$18.70	$18.70
Purchase #4	$228.58	7.771%	$246.343	$246.34	$246.35	$246.30
Purchase #5	$70.98	10.705%	$78.5784	$78.58	$78.60	$78.60
Purchase #6	$107.42	11.236%	$119.4897	$119.49	$119.50	$119.50
Purchase #7	$139.50	11.123%	$155.0166	$155.02	$155.00	$155.00
7 purchase totals =	$764.13		$837.5611	$837.56	$837.60	$837.60