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	$100.51	13.713%	$114.2929	$114.29	$114.30	$114.30
Purchase #2	$100.52	11.627%	$112.2075	$112.21	$112.20	$112.20
Purchase #3	$245.61	13.614%	$279.0473	$279.05	$279.05	$279.00
Purchase #4	$225.53	8.398%	$244.47	$244.47	$244.45	$244.50
Purchase #5	$99.88	7.631%	$107.5018	$107.50	$107.50	$107.50
Purchase #6	$145.75	4.309%	$152.0304	$152.03	$152.05	$152.00
Purchase #7	$100.58	9.302%	$109.936	$109.94	$109.95	$109.90
7 purchase totals =	$1,018.38		$1,119.4859	$1,119.49	$1,119.50	$1,119.40