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	$114.80	7.583%	$123.5053	$123.51	$123.50	$123.50
Purchase #2	$40.78	4.407%	$42.5772	$42.58	$42.60	$42.60
Purchase #3	$64.75	4.164%	$67.4462	$67.45	$67.45	$67.40
Purchase #4	$41.61	9.674%	$45.6354	$45.64	$45.65	$45.60
Purchase #5	$249.25	6.535%	$265.5385	$265.54	$265.55	$265.50
Purchase #6	$181.83	10.616%	$201.1331	$201.13	$201.15	$201.10
Purchase #7	$129.36	8.221%	$139.9947	$139.99	$140.00	$140.00
7 purchase totals =	$822.38		$885.8304	$885.84	$885.90	$885.70