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	$241.84	3.536%	$250.3915	$250.39	$250.40	$250.40
Purchase #2	$154.83	6.235%	$164.4837	$164.48	$164.50	$164.50
Purchase #3	$131.59	11.698%	$146.9834	$146.98	$147.00	$147.00
Purchase #4	$189.53	13.649%	$215.3989	$215.40	$215.40	$215.40
Purchase #5	$176.35	10.192%	$194.3236	$194.32	$194.30	$194.30
Purchase #6	$180.66	9.731%	$198.24	$198.24	$198.25	$198.20
Purchase #7	$127.51	9.353%	$139.436	$139.44	$139.45	$139.40
7 purchase totals =	$1,202.31		$1,309.2571	$1,309.25	$1,309.30	$1,309.20