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	$139.40	4.376%	$145.5001	$145.50	$145.50	$145.50
Purchase #2	$132.84	3.304%	$137.229	$137.23	$137.25	$137.20
Purchase #3	$80.75	6.174%	$85.7355	$85.74	$85.75	$85.70
Purchase #4	$196.80	9.375%	$215.25	$215.25	$215.25	$215.30
Purchase #5	$120.78	9.711%	$132.5089	$132.51	$132.50	$132.50
Purchase #6	$80.31	12.167%	$90.0813	$90.08	$90.10	$90.10
Purchase #7	$113.50	12.446%	$127.6262	$127.63	$127.65	$127.60
7 purchase totals =	$864.38		$933.9310	$933.94	$934.00	$933.90