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	$115.67	4.523%	$120.9018	$120.90	$120.90	$120.90
Purchase #2	$29.39	8.513%	$31.892	$31.89	$31.90	$31.90
Purchase #3	$132.52	4.612%	$138.6318	$138.63	$138.65	$138.60
Purchase #4	$62.36	4.150%	$64.9479	$64.95	$64.95	$64.90
Purchase #5	$105.50	9.403%	$115.4202	$115.42	$115.40	$115.40
Purchase #6	$118.58	7.458%	$127.4237	$127.42	$127.40	$127.40
Purchase #7	$82.72	9.221%	$90.3476	$90.35	$90.35	$90.30
7 purchase totals =	$646.74		$689.5650	$689.56	$689.55	$689.40