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	$242.62	12.553%	$273.0761	$273.08	$273.10	$273.10
Purchase #2	$179.44	7.731%	$193.3125	$193.31	$193.30	$193.30
Purchase #3	$134.86	12.768%	$152.0789	$152.08	$152.10	$152.10
Purchase #4	$26.77	10.108%	$29.4759	$29.48	$29.50	$29.50
Purchase #5	$42.79	5.734%	$45.2436	$45.24	$45.25	$45.20
Purchase #6	$215.37	5.180%	$226.5262	$226.53	$226.55	$226.50
Purchase #7	$106.62	4.788%	$111.725	$111.73	$111.75	$111.70
7 purchase totals =	$948.47		$1,031.4382	$1,031.45	$1,031.55	$1,031.40